Occupational Medicine · Supplementary · from Occupational Medicine

Case 3: Work-Related Carpal Tunnel Syndrome

Patient Presentation

Demographics: 38-year-old female poultry processing plant worker

Chief Complaint: "My hands go numb at night and I keep dropping things at work — it's been getting worse for about 8 months."

History of Present Illness: Ms. A.C. presents to the occupational health clinic with progressive bilateral hand numbness, tingling, and weakness, worse on the right (dominant) side. She works on a poultry processing line where she performs repetitive cutting, deboning, and trimming motions with a knife for 8-10 hours per shift, 5-6 days per week. Her job requires sustained grip force, repetitive wrist flexion and extension, and exposure to cold temperatures (processing area maintained at 4°C / 40°F).

She reports nocturnal paresthesias in the thumb, index, and middle fingers bilaterally that wake her from sleep 3-4 times per night. She shakes her hands to relieve symptoms ("flick sign" positive). During the day, she experiences numbness while performing cutting motions at work, and has noticed progressive difficulty with fine motor tasks such as buttoning shirts and picking up small objects. She dropped a knife at work twice last month and is concerned about injury risk.

Symptoms began insidiously approximately 14 months ago but have accelerated over the past 8 months since her line speed was increased by 15% due to staffing shortages. She reports that several coworkers have similar complaints. She has tried wrist splints purchased at a pharmacy with partial nighttime relief.

Past Medical History:

• Gestational diabetes during second pregnancy (resolved postpartum)
• Hypothyroidism (diagnosed 2 years ago)
• Obesity (BMI 34)
• Two uncomplicated vaginal deliveries

Medications:

• Levothyroxine 75 mcg daily
• Ibuprofen 400 mg TID PRN (self-treating hand pain)

Social History:

• Non-smoker
• No alcohol use
• Immigrated from Guatemala 12 years ago; bilingual Spanish/English
• Single mother, 2 children (ages 6 and 9)
• No hobbies requiring repetitive hand use
• Works overtime frequently due to financial necessity

Family History:

• Mother: diabetes mellitus type 2, carpal tunnel syndrome (bilateral releases)
• Father: unknown medical history

Physical Examination

• Vital Signs: BP 128/80 mmHg, HR 74 bpm, RR 14, SpO2 99%, Temp 36.6°C, BMI 34.1 kg/m²
• Hands/Wrists:
• Thenar atrophy noted on right hand (moderate); left thenar eminence mildly flattened
• Tinel sign: Positive bilaterally (right > left) — tingling in median nerve distribution with percussion at carpal tunnel
• Phalen test: Positive bilaterally at 15 seconds (right) and 25 seconds (left)
• Durkan compression test: Positive bilaterally
• Decreased two-point discrimination: Right thumb 8 mm, right index finger 7 mm (normal <6 mm); left within normal limits
• Grip strength (dynamometry): Right 18 kg, Left 24 kg (expected ~30 kg for age/sex)
• Pinch strength (tip pinch): Right 3.5 kg, Left 5.2 kg (expected ~7 kg)
• Upper extremity neurological: Sensation diminished to light touch and pinprick in median nerve distribution (thumb, index, middle finger, radial half of ring finger) bilaterally, right > left; ulnar nerve distribution intact; radial nerve distribution intact; motor testing reveals 4/5 thumb opposition and abductor pollicis brevis on right, 5-/5 on left
• Cervical spine: Full ROM, no radiculopathy signs, negative Spurling test

Workup and Results

Laboratory Studies:

Imaging/Additional Studies:

• Nerve conduction studies (NCS): Right median motor distal latency 5.8 ms (normal <4.4 ms, severely prolonged); right median sensory latency 4.2 ms (normal <3.5 ms); left median motor distal latency 4.9 ms (moderately prolonged); left median sensory latency 3.8 ms (mildly prolonged); ulnar nerve studies normal bilaterally; no evidence of proximal median neuropathy or cervical radiculopathy
• Electromyography (EMG): Fibrillation potentials and positive sharp waves in right abductor pollicis brevis (denervation changes); chronic neurogenic motor unit changes in right opponens pollicis; left APB shows mild chronic changes without active denervation
• Wrist ultrasound: Right median nerve cross-sectional area at carpal tunnel inlet: 14 mm² (normal <10 mm²); left: 12 mm²; flexor tenosynovitis with increased Doppler signal bilaterally
• Ergonomic job analysis: Task involves >30,000 repetitive cutting motions per shift; sustained grip force >4 kg; wrist deviation >30° from neutral in flexion/extension and ulnar deviation; cold exposure at 4°C; vibration exposure from knife

Clinical Image

Anatomical illustration of the carpal tunnel showing median nerve compression beneath the transverse carpal ligament, with corresponding nerve conduction study waveforms demonstrating prolonged distal latency. Source: Educational illustration.

Diagnosis

Bilateral Carpal Tunnel Syndrome — Right: Severe (with axonal loss); Left: Moderate — Occupational

Key Diagnostic Criteria:

• Classic symptoms: nocturnal paresthesias in median nerve distribution, positive flick sign, progressive weakness
• Positive provocative tests: Tinel, Phalen, Durkan compression bilaterally
• Thenar atrophy on right indicating chronic denervation
• Electrodiagnostic confirmation: prolonged median motor and sensory distal latencies bilaterally; active denervation (fibrillations) in right APB
• Temporal association with occupational exposure: high-repetition, high-force, cold-temperature work
• Ergonomic analysis confirming multiple established CTS risk factors (repetition >30/min, force, non-neutral posture, cold, vibration)
• Contributing personal risk factors: obesity, pre-diabetes, hypothyroidism, prior gestational diabetes, female sex

Treatment Plan

1. Right hand (severe with denervation):

• Urgent referral for carpal tunnel release surgery (open or endoscopic)
• Pre-operative optimization of glycemic status
• Post-operative rehabilitation: 4-6 weeks modified duty, progressive return to activity

1. Left hand (moderate without denervation):

• Neutral wrist splinting (cock-up splint) at night and during symptomatic activities
• Trial of corticosteroid injection (methylprednisolone 40 mg + 1 mL lidocaine into carpal tunnel under ultrasound guidance)
• If inadequate response at 6-8 weeks, surgical consultation

1. Workplace modifications (mandatory):

• Ergonomic redesign: ergonomic knife handles, anti-vibration tool wraps, adjustable workstation height
• Job rotation: limit continuous cutting to 2-hour intervals with 15-minute alternative task breaks
• Anti-vibration gloves; insulated gloves for cold exposure mitigation
• Reduction of line speed to previous rate; OSHA reporting of ergonomic hazard

1. Medical management of contributing conditions:

• Weight management counseling and referral to dietitian
• Monitor HbA1c; lifestyle modification for pre-diabetes prevention
• Continue levothyroxine; recheck TSH in 6 weeks
• Discontinue ibuprofen TID (GI risk); substitute topical diclofenac or acetaminophen

1. Workers' compensation: File claim for bilateral occupational CTS; schedule impairment rating after maximum medical improvement
2. Return to work: Modified duty immediately (no repetitive gripping/cutting with right hand); full duty after surgical recovery with ergonomic accommodations

Key Learning Points

• Carpal tunnel syndrome is the most common entrapment neuropathy and among the most prevalent work-related musculoskeletal disorders; occupational risk factors include repetition (>30 motions/min), force (>4 kg grip), non-neutral wrist posture, vibration, and cold exposure
• Electrodiagnostic studies (NCS/EMG) remain the gold standard for confirming CTS and grading severity; the presence of fibrillation potentials indicates active denervation and is an indication for surgical decompression
• Personal risk factors (obesity, diabetes, hypothyroidism, pregnancy, female sex) interact synergistically with occupational exposures; a condition can be both personally predisposed and occupationally aggravated
• Thenar atrophy represents irreversible motor axon loss; surgical decompression should be performed before this stage for optimal outcomes, though even patients with atrophy may benefit from surgery
• OSHA does not have a specific ergonomics standard (the 2001 Ergonomics Rule was repealed), but the General Duty Clause (Section 5(a)(1)) can be used to cite employers for recognized ergonomic hazards causing serious injury

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