Differential Diagnosis of Atrophy of Small Muscles of the Hand

Patterns of Wasting and Their Significance

• Bailey and Love's Short Practice of Surgery, Table 35.6

1. Peripheral Nerve Lesions (Most Common)

A. Ulnar Nerve Palsy

• Site of compression: Cubital tunnel (elbow) most common, or Guyon's canal (wrist)
• Muscles wasted: Hypothenar eminence, all interossei, medial two lumbricals, adductor pollicis
• Signs: Claw hand (ring & little fingers - "ulnar claw"), guttering on dorsum of hand, Froment's sign
• Causes: Elbow fracture/dislocation, prolonged compression, cubital tunnel syndrome, trauma

B. Median Nerve Palsy

• Site: Carpal tunnel (wrist) most common; also at elbow (anterior interosseous nerve, pronator teres syndrome)
• Muscles wasted: Thenar eminence (LOAF - lateral two lumbricals, opponens pollicis, abductor pollicis brevis, flexor pollicis brevis)
• Signs: Simian (ape) hand deformity, loss of thumb opposition, Tinel's and Phalen's signs in carpal tunnel syndrome
• Causes: Carpal tunnel syndrome (repetitive strain, pregnancy, hypothyroidism, acromegaly, rheumatoid arthritis), wrist fractures

C. Combined Median + Ulnar Nerve Lesion

• Affects all intrinsic muscles
• Causes: High wrist lacerations, combined entrapment, leprosy

2. Nerve Root / Spinal Cord Lesions

A. C8-T1 Nerve Root Compression

• Cause: Cervical spondylosis (C7-T1), disc prolapse, post-laminectomy
• All intrinsic muscles affected
• Associated sensory loss in C8-T1 dermatomal distribution (medial forearm, ring & little fingers)

B. T1 Root Lesion

• Classic cause of global wasting of all small muscles of the hand
• Due to: cervical rib, Pancoast tumor, apical lung carcinoma (Pancoast tumor invades the T1 root - a key surgical cause)
• Pancoast (superior sulcus) tumor - characterized by wasting of all intrinsics + Horner's syndrome (ptosis, miosis, anhidrosis) + shoulder/arm pain

C. Cervical Rib / Thoracic Outlet Syndrome

• Compresses lower brachial plexus (C8-T1 = lower trunk)
• Wasting predominantly in thenar eminence (median nerve territory more affected than ulnar in neurogenic TOS)
• Associated: subclavian artery compression, Adson's test positive

D. Brachial Plexus (Lower Trunk - Klumpke's Palsy)

• Lesion of C8-T1 lower trunk
• Wasting of all intrinsic muscles of hand + sensory loss over medial forearm + Horner's syndrome (if T1 root avulsion)
• Causes: Traction injury, birth trauma (Klumpke's), apical tumors

3. Anterior Horn Cell Disease

A. Amyotrophic Lateral Sclerosis (ALS) / Motor Neuron Disease

• Intrinsic hand wasting often an early presenting feature ("wasting of one hand")
• Characteristic combination of: LMN signs (wasting, fasciculations) + UMN signs (hyperreflexia, upgoing plantar)
• Fasciculations visible over the dorsum of the hand and tongue
• Progressive, bilateral - GOLDMAN-CECIL MEDICINE

B. Spinal Muscular Atrophy (SMA)

• Hereditary degeneration of anterior horn cells
• Distal wasting in SMA type III (Kugelberg-Welander)

C. Poliomyelitis

• Acute or post-polio syndrome
• Asymmetric, non-progressive after initial illness
• Residual wasting from anterior horn cell destruction

4. Spinal Cord Lesions

A. Syringomyelia

• Cavity in the central cord (typically cervical)
• Destroys anterior horn cells at the level of the cavity
• Presents with: cape distribution dissociated sensory loss (loss of pain and temperature but preserved touch/proprioception) + lower motor neuron wasting of hand muscles at the level of the lesion + upper motor neuron signs below
• Associated with Chiari malformation, trauma, tumors

B. Intramedullary Cervical Cord Tumor

• Ependymoma, astrocytoma
• Wasting + sensory disturbance at the level of the lesion

C. Cervical Myelopathy

• Chronic cervical spondylosis compressing the cord
• Wasting at the level of compression + spastic paraparesis below

5. Peripheral Neuropathies

A. Charcot-Marie-Tooth Disease (Hereditary Motor and Sensory Neuropathy)

• Genetic peripheral neuropathy
• Characteristically begins distally - "inverted champagne bottle" legs
• Hand intrinsics affected later in the course
• Autosomal dominant, most commonly PMP22 duplication

B. Leprosy

• Most common cause of peripheral neuropathy worldwide
• Ulnar and median nerve thickening + wasting
• Look for thickened nerves, trophic skin changes, anesthetic patches

C. Diabetic Peripheral Neuropathy

• Usually length-dependent, stocking-glove pattern
• Intrinsic hand wasting occurs in severe or diabetic amyotrophy

D. Vasculitic Neuropathy

• Mononeuritis multiplex → can affect ulnar/median nerves

6. Myopathic Causes

7. Disuse and Local Causes

• Disuse atrophy: Prolonged immobilization in a cast, complex regional pain syndrome (CRPS)
• Rheumatoid arthritis: Wasting from disuse, nerve entrapment, and joint destruction; compound palmar ganglion can compress the median nerve - S Das A Manual on Clinical Surgery
• Tuberculosis of wrist: Wasting of thenar and hypothenar muscles - S Das A Manual on Clinical Surgery
• Ischemia: Volkmann's ischemic contracture (post-compartment syndrome)

Quick Localization Summary

"CLEAN"

• C - Cervical rib / Cord (syringomyelia)
• L - Leprosy
• E - Entrapment neuropathy (combined median + ulnar)
• A - Amyotrophic lateral sclerosis / Apical lung tumor (Pancoast)
• N - Neuropathy (peripheral) / Nerve root (C8-T1)

• Yes → Mixed UMN + LMN = Motor Neuron Disease (ALS) - the only condition that combines both upper and lower motor neuron signs with no sensory loss

• Yes → Narrow by pattern:
  • Dermatomal (C8-T1) + neck pain → Nerve Root Lesion (cervical spondylosis, disc, Pancoast tumor)
  • Cape/dissociated loss (pain & temp gone, touch preserved) → Syringomyelia (central cord cavity)
  • Peripheral nerve territory (ulnar/median distribution) → Peripheral Nerve Palsy (cubital tunnel, carpal tunnel, leprosy)
  • Stocking-glove / length-dependent → Peripheral Neuropathy (CMT, diabetic, vasculitic)
• No sensory loss → Proceed to Step 3

• Yes → Anterior Horn Cell disease (ALS/polio/SMA)
• No → Check for myotonia/elevated CK → Myopathy (myotonic dystrophy, IBM) or Disuse/Local cause (CRPS, RA, immobilization)