Flail arm syndrome with cytoplasmic vacuoles in remaining anterior horn motor neurons: A peculiar variant of amyotrophic lateral sclerosis.

Flail arm (FA) syndrome, a minor subtype of amyotrophic lateral sclerosis (ALS), is characterized by progressive weakness and upper girdle wasting, but the associated pathological changes remain unclear. A 59-year-old man was admitted to our hospital with a 3-year history of upper girdle weakness. Bulbar symptom and gait disturbance gradually developed, and he was clinically diagnosed with FA syndrome. After a 10-year disease course, he died of pulmonary adenocarcinoma. Neuropathological examination revealed severe motor neuronal loss in the brain stem and anterior horn of the cervical spinal cord with bilateral pyramidal tract degeneration. The histological findings were consistent with typical ALS, including Bunina bodies and Lewy body-like and skein-like inclusions. Cytoplasmic vacuoles were found in the remaining anterior horn motor neurons of the lumbar spinal cord. This is a unique autopsy case with a long-standing clinical course that suggests that FA syndrome is an atypical form of ALS.