Nervous System & Special Senses

Mononeuropathies: median, ulnar, radial, peroneal

Clinical Overview and When to Suspect Mononeuropathy

— Median (carpal tunnel at wrist; pronator/anterior interosseous in forearm)

— Ulnar (cubital tunnel at elbow; Guyon canal at wrist)

— Radial ("Saturday night palsy" at spiral groove; posterior interosseous in forearm)

— Common peroneal (fibular) at the fibular neck

— Focal numbness/tingling in a dermatomal-mismatched but nerve-territory–matched distribution

— Painless weakness localized to one limb without UMN signs

— Symptoms reproducible by posture, repetitive task, or local pressure (sleep posture, leg crossing, tool use)

— Subacute onset after immobilization, weight loss, surgery, casting, or alcohol intoxication

— Neck/back pain radiating into limb

— Multiple nerve territories or bilateral symptoms

— Hyperreflexia, Babinski, bowel/bladder involvement

— Rapidly progressive or painful motor loss → consider mononeuritis multiplex (vasculitis, DM, HIV, leprosy)

Board pearl: On Step 3, the stem usually anchors you with a posture or activity (wrist flexion at night, elbow on armrest, crutch use, leg crossing). Map that posture to the entrapment site before reading the exam findings.

Step 3 management: Most isolated compressive mononeuropathies are managed outpatient with activity modification, splinting, and reassessment at 4–6 weeks before imaging or EMG—unlike Step 2 reflex of ordering studies immediately.

Mononeuropathy = focal dysfunction of a single peripheral nerve, usually from compression, entrapment, traction, or ischemia at an anatomically vulnerable site

Four highest-yield nerves for Step 3 ambulatory practice:

When to suspect in primary care:

Common ambulatory triggers: pregnancy, hypothyroidism, diabetes, RA, obesity, dialysis (amyloid), occupational vibration/keyboard use, prolonged squatting or bedrest

Red flags that argue against simple mononeuropathy and toward radiculopathy, plexopathy, or CNS lesion:

Presentation Patterns and Key History

— Nocturnal hand paresthesias in thumb, index, middle, radial half of ring finger

— Patient "shakes hand out" to relieve symptoms (flick sign)

— Triggered by driving, holding phone/book, typing

— Risk: pregnancy, hypothyroidism, DM, RA, obesity, dialysis amyloid, acromegaly

— Numbness in 5th and ulnar half of 4th digit

— Hand clumsiness, dropping objects, weak grip

— Provoked by prolonged elbow flexion (phone, sleeping)

— Wrist drop + finger drop after sleeping with arm over chair, intoxication, or crutch misuse

— Sensory loss over dorsal first web space

— Triceps spared (branches come off proximally)

— Foot drop, steppage gait

— Sensory loss dorsum of foot and lateral shin

— History: recent weight loss, leg casting, habitual leg crossing, prolonged squatting (gardening, childbirth), knee surgery

Key distinction: Foot drop from L5 radiculopathy includes weak hip abduction and foot inversion (tibialis posterior, L5 via tibial nerve)—peroneal palsy spares these. Ask the patient to invert the foot: preserved inversion + foot drop = peroneal; weak inversion = L5 root.

Board pearl: Ask about handedness, occupation, sleep posture, recent weight loss, and substance use—these single history items often clinch the nerve and site before any exam.

Median nerve – carpal tunnel syndrome (CTS):

Median – anterior interosseous (AIN): painless inability to make "OK sign" (weak FPL + FDP to index); pure motor, no sensory loss

Ulnar nerve – cubital tunnel:

Ulnar at Guyon canal: cyclists, hand-tool users; may spare dorsal ulnar hand sensation (dorsal cutaneous branch leaves proximal to wrist)

Radial nerve – spiral groove ("Saturday night palsy"):

Radial – posterior interosseous (PIN): finger drop without wrist drop and without sensory loss

Common peroneal at fibular neck:

Physical Exam Findings

— Sensory loss palmar thumb–index–middle, radial half ring; palm spared (palmar cutaneous branch arises proximal to tunnel)

— Weak thumb abduction/opposition; thenar atrophy in advanced disease

— Phalen (wrist flexion 60 sec), Tinel at wrist, carpal compression (Durkan) test—Durkan most sensitive/specific

— Sensory loss 5th + ulnar half 4th, including dorsal ulnar hand

— Weak finger abduction/adduction (interossei), weak thumb adduction

— Froment sign: thumb IP flexion when pinching paper (compensatory FPL via median)

— Wartenberg sign: abducted little finger

— Claw hand of ring/little fingers (worse with distal ulnar lesions—"ulnar paradox")

— Wrist drop, finger drop, weak thumb extension

— Triceps preserved, brachioradialis weak

— Sensory loss dorsal first web space

— Weak ankle dorsiflexion, eversion, toe extension

— Inversion preserved (tibial-innervated tibialis posterior)

— Sensory loss dorsum of foot and lateral lower leg

— Tinel at fibular neck

Board pearl: Thenar wasting + preserved palm sensation = CTS, not a more proximal median lesion. Thenar wasting + numb palm = pronator or higher median lesion.

Step 3 management: Document a focused exam in the chart—dermatome, motor grade (MRC 0–5), Tinel/Phalen/Froment—because billing, splint authorization, and disability paperwork hinge on it.

Median / CTS:

AIN lesion: cannot form "OK"—pinches with straight DIP/IP joints

Ulnar / cubital tunnel:

Ulnar at Guyon: spares dorsal ulnar hand sensation; may be purely motor if deep branch

Radial / spiral groove:

PIN: finger drop without wrist drop (ECRL preserved → wrist extends with radial deviation); no sensory loss

Common peroneal:

Always check reflexes (should be normal in pure mononeuropathy) and screen for UMN signs to exclude central mimics

Diagnostic Workup — Initial Labs and Bedside Studies

— HbA1c / fasting glucose (diabetes is the #1 systemic risk for entrapment)

— TSH (hypothyroidism → CTS)

— CBC, BMP (anemia, uremia)

— ESR/CRP, RF, anti-CCP, ANA if synovitis or multiple nerves

— B12, folate if mixed sensory complaints

— HIV, HCV, hepatitis panel, ANCA, cryoglobulins if mononeuritis multiplex suspected

— SPEP/UPEP, free light chains in dialysis patients or atypical CTS (amyloid)

— Pregnancy test in reproductive-age women with new CTS

— Wrist XR if prior fracture, deformity, or osteoarthritis

— Elbow XR for cubital tunnel after trauma or with valgus deformity

— Knee/fibula XR for foot drop after trauma or mass

— Measures nerve cross-sectional area at tunnel (median >10 mm² at carpal tunnel suggests CTS)

— Detects ganglia, lipomas, anomalous muscles, hematoma

— Useful when EMG is equivocal or to guide injection

Key distinction: Order labs based on which patients present with the mononeuropathy, not because mononeuropathy itself causes lab abnormalities. CTS in a thin young man should still prompt HbA1c, TSH, and consideration of amyloid—especially if bilateral.

Board pearl: Bilateral spontaneous CTS in an older man + lumbar stenosis + heart failure = screen for transthyretin (ATTR) amyloidosis—a Step 3 favorite linking peripheral and systemic disease.

Most compressive mononeuropathies are clinical diagnoses—labs and imaging are for secondary causes, not for confirming the nerve lesion itself

Targeted labs when history suggests systemic contributors:

Bedside maneuvers already covered (Phalen, Tinel, Durkan, Froment) serve as the initial "test"

Plain radiographs rarely needed first-line but consider:

Ultrasound (increasingly first-line in ambulatory neurology):

ECG and cardiac labs are not part of routine mononeuropathy workup—do not order reflexively

Diagnostic Workup — Confirmatory Electrodiagnostics and Imaging

— Diagnosis uncertain or atypical

— Considering surgery

— Need to localize lesion (e.g., ulnar at elbow vs wrist; radial at groove vs PIN)

— Distinguishing mononeuropathy from radiculopathy, plexopathy, or polyneuropathy

— Severity grading for prognosis and surgical timing

— Demyelinating compression: focal slowing or conduction block across the entrapment site, preserved amplitude distally

— Axonal loss: reduced CMAP/SNAP amplitudes, fibrillations on EMG (appear ~3 weeks after injury)

— Best obtained ≥3 weeks after acute onset for axonal lesions

— CTS: prolonged distal median sensory and motor latencies, slowed across wrist with normal ulnar

— Ulnar at elbow: conduction velocity drop >10 m/s across elbow segment

— Radial at spiral groove: conduction block at groove with normal SNAP if pure compression

— Peroneal at fibular neck: conduction block/slowing across fibular head; normal tibial study helps exclude L5 radiculopathy

— Cervical/lumbar spine if radiculopathy on the differential

— MR neurography for atypical, post-traumatic, or mass-related cases

— Brachial/lumbosacral plexus MRI when multiple nerves involved

Step 3 management: Do not send a classic mild–moderate CTS patient straight to EMG. Trial night splinting ± NSAIDs for 4–6 weeks first; reserve electrodiagnostics for failed conservative therapy, atypical features, or pre-surgical planning. This sequencing is a frequent Step 3 distractor.

Board pearl: A normal EMG/NCS does not exclude very mild CTS—clinical diagnosis still rules. Conversely, electrodiagnostic abnormalities without symptoms do not warrant treatment.

Nerve conduction studies (NCS) + electromyography (EMG) = gold standard when:

NCS findings:

Specific patterns:

MRI:

Ultrasound-guided injection can be diagnostic and therapeutic in CTS

Risk Stratification and First-Line Management Logic

— Mild: intermittent sensory symptoms, no weakness, no atrophy, normal/mildly abnormal EMG

— Moderate: persistent sensory symptoms ± mild weakness, abnormal EMG without denervation

— Severe: constant symptoms, weakness, atrophy, denervation on EMG, or acute axonal loss

— Identify and remove the offending posture/activity

— Splinting in neutral position of the involved joint

— Ergonomic correction (keyboard, tool grip, footwear)

— Short course NSAIDs for pain (not disease-modifying)

— Weight loss, glycemic control, treat hypothyroidism

— Re-evaluate at 4–6 weeks

— CTS: neutral wrist splint at night (± daytime during aggravating tasks); consider local corticosteroid injection if persistent; PT of limited benefit

— Cubital tunnel: elbow extension splint at night, avoid leaning on elbow, padded sleeve; avoid steroid injection (less effective, risk to nerve)

— Radial / Saturday night palsy: observation with cock-up wrist splint; most recover spontaneously within 6–12 weeks

— Peroneal: ankle-foot orthosis (AFO), avoid leg crossing, knee pads if occupational, weight regain if cachectic; most resolve in weeks–months

— Severe or progressive weakness/atrophy

— Denervation on EMG

— Failed 3–6 months conservative therapy

— Acute lesion from penetrating trauma, fracture, or mass

CCS pearl: In the office CCS case, advance the clock 4–6 weeks after splinting; if symptoms persist or worsen, then order EMG and refer to hand or orthopedic surgery. Jumping straight to surgery loses points.

Board pearl: Acute compressive radial palsy carries the best spontaneous prognosis of the four—reassure and splint, don't operate early.

Stratify each mononeuropathy by severity and etiology to choose conservative vs procedural path

Severity tiers:

General conservative algorithm (mild–moderate):

Nerve-specific first-line:

Surgical referral indications (any nerve):

Pharmacotherapy — First-Line Regimens

— Short courses (1–2 weeks) of ibuprofen 400–600 mg TID or naproxen 250–500 mg BID for pain

— No evidence they alter natural history of CTS or cubital tunnel

— Use cautiously in elderly, CKD, peptic ulcer, anticoagulated patients

— CTS: methylprednisolone 40 mg or triamcinolone 20–40 mg into carpal tunnel—provides symptom relief in ~70% at 1 month, ~50% at 1 year; reasonable bridge to surgery or in pregnancy

— Ultrasound guidance preferred to avoid nerve injury

— Limit to 2–3 injections per site per year

— Avoid in cubital tunnel (limited benefit, risk of ulnar nerve injury) and generally avoid in radial/peroneal compressions

— Gabapentin 100–300 mg qhs titrated to 900–1800 mg/day in divided doses

— Pregabalin 75 mg BID, titrate to 150–300 mg/day

— Duloxetine 30–60 mg daily, especially if comorbid depression or diabetic neuropathy

— Tricyclics (nortriptyline 10–25 mg qhs) cheaper but anticholinergic in elderly

— Levothyroxine for hypothyroidism

— Glycemic optimization in DM

— Diuresis/compression for fluid-overload CTS

Step 3 management: For pregnancy-related CTS, start with nocturnal splinting; if refractory, local steroid injection is acceptable in 2nd/3rd trimester. Most cases resolve postpartum—reassurance is part of the prescription.

Board pearl: Gabapentin requires renal dose adjustment (CrCl <60).

Mononeuropathies are mechanical, so pharmacotherapy is adjunctive—drugs do not replace splinting, activity modification, or surgery

NSAIDs:

Local corticosteroid injection:

Neuropathic pain agents (for persistent paresthesias/burning):

Vitamin B6 historically used in CTS—evidence weak; avoid doses >100 mg/day (paradoxical sensory neuropathy)

Oral steroids: short prednisone tapers (20 mg × 2 weeks then taper) help CTS transiently—rarely used due to systemic side effects

Treat underlying systemic disease:

Procedures and Surgical Management

— Open or endoscopic division of transverse carpal ligament

— Outcomes similar; endoscopic = faster return to work, slightly higher transient nerve injury

— >90% symptom relief; recurrence rare

— Post-op: light activity in days, full strength by 6–12 weeks

— In situ decompression (first choice, especially mild–moderate)

— Anterior transposition (subcutaneous or submuscular) if subluxation or severe disease

— Medial epicondylectomy in select cases

— Recovery slower than CTR; sensory improvement may take months

— Surgery rarely needed for Saturday night palsy

— Indicated for penetrating injury, displaced humeral shaft fracture with persistent palsy >3–6 months, or PIN entrapment by tumor/synovitis

— Tendon transfers if no recovery at 12–18 months

— Decompression at fibular head if persistent symptoms >3 months or progressive deficit

— Excise mass lesions (ganglion, lipoma, schwannoma)

— Tendon transfer (posterior tibialis to dorsum) for permanent foot drop

— Realistic expectations: sensory recovery > motor; chronic atrophy may not reverse

— Risks: incomplete relief, scar tenderness, pillar pain (CTR), infection, recurrence

— Anticoagulation management per ACC perioperative guidelines

— Wound check 7–14 days

— Hand/occupational therapy referral as needed

— Return-to-work counseling: desk work in days, manual labor in 4–6 weeks

CCS pearl: After CTR, schedule a 2-week wound visit and a 6-week functional assessment. Order occupational therapy for grip strengthening and scar desensitization—both are exam-favored CCS orders.

Board pearl: Persistent symptoms after CTR most often reflect incomplete release or missed double-crush (coexistent C6–C7 radiculopathy).

Surgery is indicated when conservative care fails, weakness/atrophy progresses, or EMG shows axonal loss

Carpal tunnel release (CTR):

Cubital tunnel surgery:

Radial nerve:

Peroneal nerve:

Pre-op counseling:

Post-procedural follow-up:

Special Populations — Elderly and Renal/Hepatic Impairment

— Higher baseline polyneuropathy from age, DM, B12 deficiency—may mask or mimic focal mononeuropathy

— Thenar/hypothenar atrophy may be advanced at presentation; lower threshold for EMG and surgical referral

— Falls risk with foot drop—prioritize AFO and PT to prevent injury

— NSAID caution: GI bleed, renal impairment, HTN exacerbation, drug interactions (anticoagulants, SSRIs)

— Gabapentin/pregabalin: start low (gabapentin 100 mg qhs), titrate slowly; sedation and falls are leading adverse effects

— Tricyclics: avoid per Beers criteria when possible (anticholinergic, orthostasis)

— Steroid injections: acceptable but watch for hyperglycemia in diabetics for 5–7 days

— Long-term hemodialysis predisposes to β2-microglobulin amyloid CTS, often bilateral

— Surgery is effective but wound healing slower

— Gabapentin: major renal adjustment—CrCl 30–59: 400–1400 mg/day; CrCl 15–29: 200–700 mg/day; HD: 100–300 mg post-dialysis

— Pregabalin: also renally cleared; reduce dose by 50% at CrCl 30–60

— Avoid NSAIDs in CKD stage 3b–5

— Duloxetine: avoid if CrCl <30

— Duloxetine contraindicated in chronic liver disease/cirrhosis

— Tricyclics: reduce dose, monitor sedation

— Acetaminophen preferred analgesic; cap at 2 g/day in cirrhosis

— Local steroid injections safe

— In limited-life-expectancy patients, prioritize splinting, AFO, and pain control over surgery

— Shared decision-making about CTR in mild cognitive impairment—home post-op care must be feasible

Step 3 management: A 72-year-old dialysis patient with bilateral nocturnal hand numbness needs CTS evaluation and SPEP, not just "diabetic neuropathy" labeling—dialysis amyloid is a high-yield distractor target.

Board pearl: Always re-check renal function before titrating gabapentinoids in elderly.

Elderly considerations:

CKD / dialysis:

Hepatic impairment:

Frailty and goals of care:

Special Populations — Pregnancy, Pediatrics, Athletes, Occupational

— CTS occurs in up to 30–60% of pregnant women, peaks third trimester from fluid retention

— First-line: nocturnal neutral wrist splinting; reassurance that >80% resolve within weeks postpartum

— Avoid NSAIDs after 20 weeks (oligohydramnios) and after 30 weeks (ductus closure)

— Acetaminophen acceptable for pain

— Local steroid injection (triamcinolone) reasonable if refractory in 2nd/3rd trimester

— Surgery rarely needed during pregnancy

— Meralgia paresthetica (lateral femoral cutaneous neuropathy) and peroneal palsy from prolonged lithotomy are pregnancy-adjacent boards favorites

— Mononeuropathies uncommon; consider hereditary neuropathy with liability to pressure palsies (HNPP) in recurrent painless palsies (PMP22 deletion, AD)

— Neonatal brachial plexopathy (Erb, Klumpke) is separate—not a true mononeuropathy but tested adjacent

— Backpack palsy: long thoracic or brachial plexus traction

— Cyclists: ulnar neuropathy at Guyon canal (handlebar palsy)—pad grips, change hand position

— Throwing athletes: ulnar at cubital tunnel from valgus stress

— Runners with tight footwear: tarsal tunnel, deep peroneal at ankle

— CTS: assembly line, dental hygiene, sign language interpreters, prolonged keyboarding

— Document for workers' compensation—ergonomic assessment, job modification, OSHA reporting where applicable

— Vibration exposure (jackhammer) → median and ulnar neuropathies plus hand-arm vibration syndrome

— Loss of fat pad over fibular head → peroneal palsy

— Counsel on leg-crossing avoidance, padded chairs

Board pearl: Recurrent painless mononeuropathies at multiple typical compression sites in a young patient with family history = HNPP—order PMP22 deletion testing.

Step 3 management: For pregnancy CTS, document conservative trial and postpartum follow-up at the 6-week visit—avoids unnecessary surgical referrals.

Pregnancy:

Pediatrics:

Athletes:

Occupational:

Bariatric / rapid weight loss:

Complications and Adverse Outcomes

— Delayed decompression past the window of reversible axonal injury → persistent weakness, atrophy

— CTS: thenar atrophy, weak opposition → loss of pinch and fine motor control

— Cubital tunnel: clawing, weak grip, loss of dexterity

— Radial: residual wrist drop limiting employment

— Peroneal: chronic foot drop, falls, tripping injuries

— Persistent paresthesias, allodynia, neuropathic pain

— Anesthetic skin → unrecognized burns, ulcers (especially in DM)

— Disproportionate burning pain, autonomic changes, trophic skin/nail changes

— May follow nerve injury or surgery—early PT, multidisciplinary pain referral

— Foot drop dramatically increases fall risk in elderly—major source of morbidity

— Hand weakness → dropped objects, scald injuries

— CTR: pillar pain, scar tenderness, incomplete release, recurrent CTS, rare median nerve laceration

— Cubital tunnel surgery: ulnar nerve subluxation, hematoma, infection, persistent symptoms

— Peroneal decompression: incomplete recovery if delayed

— Gabapentinoids: sedation, falls, weight gain, edema, dependence (Schedule V pregabalin)

— Steroid injection: tendon rupture, infection, depigmentation, transient hyperglycemia, rare nerve injury

— NSAIDs: GI bleed, AKI, HTN

— Lost wages, occupational disability

— Depression and anxiety with chronic pain

— Coexistent proximal (cervical radiculopathy) and distal (CTS) compression amplifies symptoms and worsens surgical outcomes

Key distinction: Postoperative pillar pain (lateral palmar tenderness after CTR) is expected, peaks at 2–3 months, and resolves—not a complication requiring re-operation. Distinguish from persistent median symptoms suggesting incomplete release.

Board pearl: Any post-injury limb with burning pain out of proportion + skin/temp change → think CRPS and refer early to pain medicine.

Permanent motor deficit:

Sensory complications:

Complex regional pain syndrome (CRPS):

Falls and fractures:

Surgical complications:

Pharmacologic complications:

Psychosocial:

Double crush phenomenon:

When to Escalate Care

— Acute traumatic nerve injury (laceration, displaced fracture, gunshot) → emergency hand/orthopedic surgery

— Open wound with motor deficit

— Compartment syndrome features (severe pain, pallor, pulselessness, paresthesias, paralysis)

— Acute foot drop after knee dislocation or trauma → vascular and orthopedic evaluation

— Rapidly progressive multifocal deficits → consider vasculitic mononeuritis multiplex (admit, neurology consult, possible biopsy and immunosuppression)

— Diagnostic uncertainty

— Atypical distribution or progression

— Multiple nerve involvement

— Suspected hereditary neuropathy (HNPP)

— Failure of conservative therapy at 6 weeks

— Severe CTS with thenar atrophy

— Cubital tunnel with intrinsic weakness or denervation

— Persistent radial palsy >3 months, especially with humeral fracture

— Peroneal palsy with mass lesion, trauma, or no recovery at 3 months

— Splint fabrication and fitting

— AFO for foot drop

— Hand therapy for desensitization, scar management, strengthening

— Workplace ergonomic evaluation

— Refractory neuropathic pain despite first-line agents

— Suspected CRPS

— Mononeuritis multiplex (vasculitis, HIV, HCV, leprosy, sarcoidosis)

CCS pearl: On the case interface, the right escalation order is often "Refer to hand surgery, non-urgent" plus "Occupational therapy referral"—both should be selected for severe CTS, not just one.

Step 3 management: Document specific triggers (atrophy, denervation, failed 6-week trial) in the referral note—insurance authorization and Step 3 stems both reward this specificity.

Most mononeuropathies are managed entirely in primary care; escalation triggers are specific

Urgent (same-day) escalation:

Subacute referral to neurology:

Referral to hand or orthopedic surgery:

Referral to PM&R / occupational therapy:

Pain medicine referral:

Rheumatology / ID consult:

Key Differentials — Same-Category (Neuropathic) Causes

— Neck pain radiating down arm

— Deficits follow myotome/dermatome, not nerve distribution

— Diminished reflexes (biceps C5–6, triceps C7, brachioradialis C6)

— Spurling sign positive

— MRI cervical spine; EMG shows paraspinal denervation

— L5 radiculopathy: foot drop + weak inversion + weak hip abduction; back pain ± positive straight leg raise

— Peroneal palsy: foot drop + preserved inversion, no back pain

— Multiple nerves, often after trauma, radiation, or Parsonage-Turner syndrome (acute painful brachial neuritis followed by patchy weakness)

— EMG and MRI plexus clinch diagnosis

— Diabetic amyotrophy (Bruns-Garland): proximal thigh pain, quadriceps wasting, weight loss in older diabetic

— Retroperitoneal hematoma in anticoagulated patient → femoral neuropathy

— Diabetic, alcoholic, B12, chemotherapy

— Symmetric, distal, stocking-glove

— May coexist with mononeuropathy (double crush)

— Sequential/simultaneous involvement of named nerves

— Causes: PAN, GPA, EGPA, RA, SLE, cryoglobulinemia, HIV, HCV, leprosy, DM, sarcoid

— Workup: ANCA, ANA, RF, cryoglobulins, HIV, HCV, ESR/CRP, nerve biopsy

— HNPP: recurrent painless palsies, autosomal dominant

— CMT: chronic distal weakness, pes cavus, hammertoes, family history

— Mixed UMN/LMN signs, fasciculations, no sensory loss

Key distinction: Pure motor deficit with no sensory symptoms across multiple muscle groups → consider ALS or multifocal motor neuropathy (responds to IVIG), not simple mononeuropathy.

Board pearl: L5 radiculopathy vs peroneal palsy is the highest-yield Step 3 discriminator—test foot inversion every time.

Cervical radiculopathy (mimics median/ulnar/radial):

Lumbosacral radiculopathy (mimics peroneal):

Brachial plexopathy:

Lumbosacral plexopathy:

Polyneuropathy:

Mononeuritis multiplex:

Hereditary neuropathies:

Motor neuron disease (ALS):

Key Differentials — Other-Category Causes

— Sudden weakness with UMN signs (hyperreflexia, Babinski, spasticity later)

— Cortical sensory loss (graphesthesia, stereognosis)

— Cranial nerve involvement, dysarthria, gaze deviation

— Time-sensitive: stroke protocol if within tPA/thrombectomy window

— Subacute focal weakness or sensory loss with optic neuritis, INO, Lhermitte

— MRI brain/cord with demyelinating plaques

— Bilateral or band-like sensory level

— Bowel/bladder dysfunction

— Hyperreflexia below lesion

— Inconsistent exam, Hoover sign, give-way weakness

— Diagnosed by positive features, not exclusion

— De Quervain tenosynovitis: radial wrist pain, positive Finkelstein, no neurologic deficit—not CTS

— Lateral epicondylitis: pain at lateral elbow, no nerve symptoms

— Trigger finger: locking digit, palpable nodule

— Hip osteoarthritis: groin pain mimicking femoral neuropathy

— Tarsal tunnel syndrome: medial ankle pain, plantar foot paresthesias (not peroneal)

— Acute limb ischemia: pain, pallor, pulselessness—pain precedes neurologic deficit

— Thoracic outlet syndrome: positional arm symptoms, ± vascular signs

— Lyme: facial palsy, radiculoneuritis, history of tick exposure/rash

— Herpes zoster: dermatomal vesicles, postherpetic neuralgia

— Leprosy (globally common): thickened nerves, hypopigmented anesthetic patches

— Pancoast tumor → lower brachial plexopathy + Horner syndrome

— Schwannoma, neurofibroma at nerve sites

— Lead → wrist drop (mimics radial palsy)

— Heavy alcohol use → compressive radial palsy + alcoholic polyneuropathy

Board pearl: Wrist drop in a painter or battery worker = consider lead toxicity—check blood lead level.

Key distinction: UMN signs (hyperreflexia, Babinski) exclude isolated peripheral mononeuropathy—image the CNS immediately.

Stroke / TIA:

Multiple sclerosis:

Spinal cord lesion:

Functional (conversion) neurologic disorder:

Musculoskeletal mimics:

Vascular:

Infectious:

Tumor:

Toxic/metabolic:

Secondary Prevention and Long-Term Plan

— Glycemic control (A1c target individualized, typically <7%) to reduce both polyneuropathy and entrapment risk

— Weight management—obesity strongly linked to CTS

— Thyroid replacement in hypothyroidism

— Treat inflammatory arthritis with DMARDs to reduce tenosynovitis

— Smoking cessation (impairs nerve healing)

— Limit alcohol (compressive and toxic neuropathy)

— Neutral wrist posture during keyboarding; ergonomic keyboard, vertical mouse

— Avoid prolonged elbow flexion >90° (phone use, sleeping with bent elbow)

— Padded elbow rest, avoid leaning on elbows

— Cyclists: padded gloves, vary hand position

— Avoid habitual leg crossing; padded chairs for those who squat or kneel occupationally

— Properly fitted crutches (axillary pad position) to prevent radial palsy

— Most patients require only acetaminophen or short NSAID course after CTR or cubital release

— Limit opioids to 3–5 days, prescribe with multimodal analgesia plan

— Continue treatment of underlying systemic disease

— Replace worn splints; ensure proper fit

— Continue AFO until functional recovery in peroneal palsy

— Modified duty letter with specific restrictions and review date

— Vocational rehabilitation referral if persistent disability

— Document for workers' comp claims when occupational

— Warning signs of recurrence: returning numbness, weakness, atrophy

— When to call: new motor weakness, fevers post-op, worsening pain

Step 3 management: Add an A1c check, TSH, and BMI counseling at the CTS follow-up visit—Step 3 rewards integrating chronic disease management with the presenting complaint.

Board pearl: Adequate splinting compliance is the strongest predictor of conservative success in CTS—directly ask and reinforce at every visit.

Address modifiable risk factors:

Ergonomic and behavioral interventions:

Discharge / post-op medications:

Splint and orthotic maintenance:

Workplace plan:

Patient education:

Follow-Up, Monitoring, and Rehabilitation

— Initial visit: diagnosis, splint, education, lab workup

— 4–6 weeks: assess response; if improved, continue and recheck at 3 months; if no improvement, consider EMG and specialist referral

— 3 months: reassess; persistent or progressive symptoms → escalate

— 6 months: chronic management plan, surgical consideration

— Wound check at 7–14 days (suture removal, infection screen)

— 4–6 weeks: range of motion, return-to-work assessment

— 3 months: functional outcome, grip strength, sensory recovery

— 6–12 months: final outcome; persistent symptoms warrant repeat EMG

— Symptom diary: frequency, severity, nocturnal awakenings

— Grip and pinch strength (dynamometer)

— Two-point discrimination (normal <6 mm fingertip)

— MRC motor grading of affected muscles

— Functional scales (Boston Carpal Tunnel Questionnaire, DASH)

— Occupational therapy for hand mononeuropathies—nerve gliding exercises, edema control, scar management, ergonomic training

— Physical therapy for peroneal palsy—gait training, AFO fitting, balance work to prevent falls

— Strength rehab post-op once tissue healed (typically 4–6 weeks)

— Desensitization for residual paresthesias

— Realistic timeline: sensory recovery in weeks–months; motor recovery slower; chronic atrophy may not fully reverse

— Recurrence risk and prevention

— Driving restrictions after surgery (~2 weeks for desk-job patients, longer for manual operators)

— Mental health screening for chronic pain

CCS pearl: Reorder "functional status assessment" and "occupational therapy" at the 6-week post-op visit—both are high-value CCS actions for hand mononeuropathies.

Board pearl: If symptoms recur >6 months after initially successful CTR, suspect scar adhesion, incomplete release, or new pathology—reimage and re-EMG.

Conservative management follow-up cadence:

Post-operative follow-up:

Monitoring parameters:

Rehabilitation:

Counseling topics:

Ethical, Legal, and Patient Safety Considerations

— Disclose realistic outcomes: ~90% symptom relief for CTR, lower for severe disease with atrophy

— Discuss alternatives: continued conservative care, injection, expectant management

— Document understanding of risks (incomplete relief, infection, nerve injury, recurrence)

— Special consideration in patients with cognitive impairment—involve surrogate decision-maker per state law; assess decisional capacity, not just diagnosis

— Mononeuropathies linked to work tasks may be reportable occupational illnesses (OSHA 300 log if employer subject)

— Provide objective documentation of work-relatedness; avoid both over- and under-attribution

— Maintain therapeutic relationship distinct from disability adjudication—patients may perceive conflict

— Workers' comp patients often have different reimbursement and follow-up rules; confirm coverage before EMG/surgery to prevent denied claims

— Provide specific restrictions (no lifting >10 lbs, no repetitive gripping) with end dates

— Reassess at each visit; indefinite restrictions risk deconditioning and dependence

— Counsel patients with foot drop, hand weakness, or post-op splints not to drive until cleared

— Document the conversation

— Suspected elder abuse if pressure-related neuropathy from neglect (immobilization, prolonged restraint) → report per state law

— Lead toxicity is reportable in most states

— Surgical patients discharged on opioids need clear taper plan, safe storage education, and follow-up call within 72 hours

— Communicate splint/AFO needs to home health and rehab to avoid lapse in protection

— Reconcile renally adjusted gabapentinoids when transitioning from inpatient to outpatient

— Manual laborers and low-wage workers face higher CTS incidence and greater financial impact from lost work—advocate for ergonomic accommodation

Step 3 management: A confused, restrained ICU patient who develops bilateral wrist drops requires incident report, restraint review, and possibly Adult Protective Services consideration if in a long-term care setting—safety culture is testable.

Informed consent for surgery:

Workers' compensation and occupational reporting:

Disability and return-to-work:

Driving safety:

Mandatory reporting:

Transition-of-care safety:

Health equity:

High-Yield Associations and Rapid-Fire Facts

Board pearl: Step 3 stems use posture vignettes—match the posture to the nerve before reading the exam to save time.

CTS associations: pregnancy, hypothyroidism, DM, RA, obesity, acromegaly, amyloidosis (dialysis, ATTR), mucopolysaccharidoses

Recurrent painless palsies + family history = HNPP (PMP22 deletion)

Mononeuritis multiplex etiologies: DM, PAN, GPA, EGPA, cryoglobulinemia, RA, SLE, HIV, HCV, leprosy, sarcoid

Wrist drop differential: radial nerve compression > humeral fracture > lead toxicity > vasculitis

Foot drop differential: peroneal at fibular neck > L5 radiculopathy > sciatic injury > ALS > stroke (UMN signs)

Saturday night palsy: spiral groove radial compression; triceps spared (proximal branch)

Honeymoon palsy: radial compression from partner's head on arm

Crutch palsy: axillary radial compression from poor crutch use

Handlebar palsy: ulnar at Guyon canal in cyclists

Tardy ulnar palsy: ulnar neuropathy years after childhood elbow fracture with cubitus valgus

Ulnar paradox: more distal ulnar lesions cause worse clawing (intact FDP to 4th/5th)

Froment sign: thumb IP flexion when pinching paper → ulnar neuropathy

Wartenberg sign: persistently abducted little finger → ulnar

Pope's blessing / hand of benediction: proximal median lesion (can't flex index/middle when making fist)

OK sign failure: AIN syndrome

Pinch sign: AIN; thumb and index pinch with extended DIPs

Tinel sign location localizes entrapment site

Phalen, Durkan, Tinel for CTS—Durkan most sensitive

Pancoast tumor: lower trunk brachial plexopathy + Horner + apical lung mass

Diabetic amyotrophy: thigh pain, quad wasting, weight loss in older T2DM

Parsonage-Turner: post-viral/post-vaccine acute painful brachial neuritis → patchy weakness

Meralgia paresthetica: lateral femoral cutaneous neuropathy at inguinal ligament—obese, tight belts, pregnancy

Tarsal tunnel: posterior tibial nerve at medial ankle → plantar foot burning

Best prognosis: Saturday night radial palsy (>90% spontaneous recovery)

Worst prognosis: axonal injury with denervation on EMG, delayed decompression

Board Question Stem Patterns

— Answer: Neutral wrist splint at night; EMG/surgery only if refractory

— Distractor: Immediate surgical referral

— Answer: Common peroneal at fibular neck; conservative care, AFO

— Distractor: MRI lumbar spine (would be answer if inversion weak + back pain)

— Answer: Observation + wrist cock-up splint; expect recovery in 6–12 weeks

— Distractor: Surgical exploration

— Answer: Elbow extension splint at night, padded sleeve, avoid leaning

— Distractor: Steroid injection at elbow

— Answer: Anterior interosseous neuropathy; observation, EMG if no recovery

— Answer: PMP22 deletion testing; lifestyle modification

— Answer: Cryoglobulinemic vasculitis; rheum consult, immunosuppression, treat HCV

— Answer: Blood lead level, chelation

— Answer: β2-microglobulin amyloid; surgical release effective

— Answer: Chest imaging for apical lung tumor

Step 3 management: When the stem includes posture + specific muscle deficit + classic sensory map, answer with conservative management first unless severe weakness, atrophy, or denervation is described.

Board pearl: "Preserved triceps" is the radial nerve stem's signature.

Stem 1 — Classic CTS: Middle-aged pregnant or hypothyroid woman with nocturnal hand numbness shaken out, decreased thumb opposition, thenar atrophy

Stem 2 — Foot drop discriminator: Patient lost weight, crosses legs, develops foot drop with preserved inversion and no back pain

Stem 3 — Saturday night palsy: Intoxicated patient slept with arm over chair, wakes with wrist and finger drop, intact triceps

Stem 4 — Cubital tunnel: Office worker leans on elbow, develops 4th/5th finger numbness, weak grip, positive Froment

Stem 5 — AIN syndrome: Painless inability to form OK sign, no sensory loss

Stem 6 — HNPP: Young adult with recurrent painless palsies at typical compression sites, family history

Stem 7 — Mononeuritis multiplex: Hepatitis C patient with sequential foot drop and wrist drop, palpable purpura

Stem 8 — Lead toxicity: Battery worker with bilateral wrist drop and microcytic anemia

Stem 9 — Dialysis amyloid: Long-term HD patient with bilateral CTS

Stem 10 — Pancoast: Heavy smoker with shoulder/arm pain, hand wasting, ptosis/miosis

One-Line Recap

Mononeuropathies are focal, posture- or task-driven compressions of single nerves diagnosed clinically by mapping the patient's history and exam to a specific entrapment site, managed first with splinting/orthotics and risk-factor modification, and escalated to EMG and surgery only when weakness, atrophy, denervation, or refractory symptoms emerge.

— CTS spares palm sensation; pure motor median = AIN

— Saturday night radial palsy spares triceps; PIN spares wrist extension and sensation

— Distal ulnar lesions cause worse clawing (ulnar paradox); Froment and Wartenberg signs

— Peroneal foot drop preserves inversion and hip abduction—if those are weak, image the spine for L5 radiculopathy

Board pearl: On Step 3, the highest-yield decision is not which nerve—it's choosing splinting and follow-up over premature EMG or surgery in the typical ambulatory stem, while still recognizing the rare red flags (vasculitis, amyloid, lead, Pancoast, HNPP) that change the entire pathway.

Localize before you test: posture + dermatome + motor map → nerve and site; reserve EMG for atypical, severe, or pre-surgical cases

Conservative first: neutral splints (wrist for median, elbow extension for ulnar, AFO for peroneal), activity modification, and treatment of underlying systemic disease (DM, hypothyroidism, RA, obesity) deliver the majority of cures over 4–6 weeks

High-yield discriminators:

Escalate when: atrophy, denervation on EMG, multifocal nerves (mononeuritis multiplex), traumatic laceration, progressive weakness, or failed 3–6 months conservative care—then refer to hand/orthopedic surgery, neurology, or rheumatology as indicated