Inclusion body myositis masquerading as amyotrophic lateral sclerosis.

diagnosis with a relentless progression toward death. Inclusion body myositis (IBM) is often cited as a common mimicker of ALS1, although literature to support this is scant. Despite extensive diagnostic evaluation, without a muscle biopsy, misdiagnoses may still occur. As we will discuss, patients with IBM may have hyperreflexia and fasciculations which are often mistaken for signs of motor neuron disease. The distinctive pattern of weakness in IBM, particularly the weakness of finger flexion, may be initially lacking. Lastly, spontaneous activity and large, long duration motor units may be seen on electromyography (EMG). These findings may be interpreted as "neuropathic" and contribute to diagnostic error.2 We report two patients who were initially diagnosed with ALS, but on reevaluation at the ALS clinic, were confirmed to have IBM.