Inclusion Body Myositis Mimicking Bilateral Anterior Interosseous Neuropathies.

Anterior interosseous neuropathy is a rare cause of weakness of flexion of the thumb interphalangeal and index and middle finger distal interphalangeal joints, most commonly caused by trauma, compression, or inflammation. Bilateral anterior interosseous nerve palsies are rare, and other neuromuscular disorders may present with a similar pattern of weakness. We describe 2 patients who initially presented for orthopedic evaluation for suspected anterior interosseous neuropathy and were subsequently diagnosed with inclusion body myositis, an uncommon inflammatory myopathy affecting adults, with a predilection for finger and thumb flexor muscles. Electromyography, serologic and radiographic studies, and muscle biopsy can aid in diagnosis and help to distinguish inclusion body myositis from an anterior interosseous neuropathy.