Myopathic dropped head syndrome: an expanding clinicopathological spectrum.

Objective: A number of neuromuscular conditions may lead to a dropped head syndrome (DHS), with some patients developing a late onset noninflammatory myopathy affecting only, or predominantly, neck extensor muscles (NEM). The cause, pathogenesis, and nosological classification of this condition are unclear. To further investigate this condition, the authors evaluated the clinical, electrodiagnostic and pathologic findings in seven patients with a myopathic DHS.

Design: Analysis of clinical data, electrodiagnostic studies, and muscle biopsies of seven patients, including one set of identical twins, who developed a very late onset myopathy with severe NEM weakness.

Results: Age of onset was 61-79 yrs, with the pair of identical twins developing NEM weakness within 1 yr of each other (ages 63 and 64, respectively). Seven patients developed weakness (six slight weakness and one more severe) in muscles other than NEM. The group was characterized by the electromyography (EMG) showing a "myopathic" pattern in cervical paraspinal muscles (7/7), muscle biopsies with nonspecific myopathic changes on histologic stains (7/7), marked abnormalities in NADH dehydrogenase-reacted sections (6/7), desmin-positive sarcoplasmic deposits (1/7), low carnitine levels by biochemical assays (2/7), and mitochondrial changes (3/7).

Conclusions: Myopathic DHS encompasses a wide spectrum of conditions that strongly affect NEM; however, as documented in the monozygotic twins, some patients may suffer from a distinct, genetically determined form of late-onset restricted myopathy leading clinically to DHS.