What causes numbness in the palm, especially in adults with a history of conditions like diabetes or repetitive strain injuries?

Palmar Numbness: Causes and Diagnostic Approach

Primary Causes

Carpal tunnel syndrome is the most common cause of palmar numbness, resulting from median nerve compression at the wrist and typically presenting with numbness in the thumb, index, middle, and radial half of the ring finger. 1, 2

Nerve Entrapment Syndromes

• Carpal tunnel syndrome affects the median nerve distribution (thumb, index, middle fingers, and radial half of ring finger) with classic nocturnal pain, tingling, and numbness that may be reproduced by wrist hyperflexion or median nerve percussion 1, 2
• Ulnar tunnel syndrome causes numbness of the little finger and ulnar aspect of the ring finger, with potential intrinsic muscle weakness 2
• Nerve entrapment can occur anywhere from the brachial plexus to the fingers, with trauma and compression being common precipitating factors 2

Diabetic Peripheral Neuropathy

• Diabetic neuropathy typically presents with distal symmetric sensory symptoms beginning in the toes and feet, progressing proximally in a length-dependent pattern, though it can affect the hands in advanced cases 3, 4
• Small-fiber involvement causes burning, tingling, and pain, while large-fiber involvement produces numbness and loss of protective sensation 3, 4
• Up to 50% of diabetic peripheral neuropathy may be asymptomatic, making screening essential even without complaints 3, 4
• Assessment should include pinprick and temperature sensation (small-fiber function), vibration perception using 128-Hz tuning fork (large-fiber function), and 10-g monofilament testing 3

Vascular Causes

• Thrombosis of a persistent median artery (rare anatomic variation) can cause acute carpal tunnel syndrome with numbness, coldness, and acute hand swelling 5
• Vascular causes should be suspected when patients present with unusual features like coldness and acute swelling, confirmed by ultrasound Doppler 5

Risk Factors to Assess

• Diabetes mellitus increases risk for both diabetic neuropathy and nerve entrapment syndromes 2, 3
• Smoking, alcohol consumption, rheumatoid arthritis, and hypothyroidism are risk factors for nerve entrapment, though these typically produce bilateral symptoms 2
• Occupational exposure to high pressure, high force, repetitive work, and vibrating tools increases carpal tunnel syndrome risk 1
• Obesity should be excluded before attributing symptoms to occupational causes 1

Diagnostic Approach

History Elements

• Determine the specific distribution of numbness: median nerve (thumb, index, middle fingers) suggests carpal tunnel syndrome; ulnar nerve (little finger, ulnar ring finger) suggests ulnar nerve pathology 2
• Assess for nocturnal symptoms, which are classic for carpal tunnel syndrome 1
• Evaluate diabetes duration, glycemic control, presence of retinopathy or renal disease, and smoking history 3
• Distinguish acute onset (days) from gradual progression (months to years), as acute presentations may indicate vascular causes or inflammatory neuropathies requiring urgent management 5, 6

Physical Examination

• Perform wrist hyperflexion test and median nerve percussion to reproduce carpal tunnel syndrome symptoms 1, 2
• Test pain sensation in specific nerve distributions: decreased sensation in thumb, index, and middle fingers suggests median nerve involvement 2
• Assess for thenar muscle weakness, which indicates advanced carpal tunnel syndrome 7
• Evaluate for intrinsic muscle weakness with ulnar nerve involvement 2
• Check for coldness and acute hand swelling, which suggest vascular causes 5

Confirmatory Testing

• Nerve conduction studies are the gold standard for diagnosing carpal tunnel syndrome, though false positives and negatives can occur 1
• Ultrasound Doppler should be obtained when vascular causes are suspected, showing nerve enlargement, hypoechogenic nerve, and intraneural vascularity 5, 8
• Electromyography and radiography help differentiate between cervical radiculopathy, thoracic outlet syndrome, and peripheral nerve entrapment 2

Critical Pitfalls to Avoid

• Failing to recognize that diabetic neuropathy is a diagnosis of exclusion—nondiabetic neuropathies may be present in patients with diabetes and may be treatable 3
• Missing acute presentations requiring urgent intervention: acute carpal tunnel syndrome from vascular thrombosis, Guillain-Barré syndrome, or vasculitis 5, 8
• Attributing symptoms to occupation without first excluding intrinsic factors like obesity, diabetes, and other systemic conditions 1
• Relying solely on physical examination tests or nerve conduction studies—diagnosis should integrate history, examination, and electrophysiological studies 1
• Overlooking that symptoms may be completely asymptomatic in up to 50% of diabetic neuropathy cases, requiring systematic screening 3, 4