Aetiology

Spinal cord lesions at T1 level:

• syringomyelia
• compression of T1 segment due to cervical spondylosis, neurofibroma
• tumour
• motor neurone disease

Root lesions eg T1 compression by a disc lesion

Brachial plexus lesions:

• trauma, irradiation, infiltration
• thoracic outlet obstruction
• Klumpke's paralysis

Peripheral nerve lesions:

• median lesions, ulnar nerve lesions
• peripheral motor neuropathy

Myopathy:

• distal myopathy
• myotonic dystrophy (forearms are more often affected than the hands)

Trophic disorders:

• disuse eg arthritis
• ischaemia eg vasculitis
• shoulder-hand syndrome

Note that in discriminating an ulnar nerve lesion from a T1 root lesion remember that in a T1 root lesion there is no sensory loss that affects the hand.