Background: Hirayama disease (HD) is a segmental nonprogressive spinal muscular atrophy found in male patients.
Objective: To report the results of a comprehensive evaluation of clinical, magnetic resonance imaging (MRI), electromyography (EMG), and survival motor neuron (SMN) gene analysis of HD.
Design: Clinical, MRI, and SMN gene deletion study.
Setting: Tertiary care teaching hospital.
Patients: Patients with HD diagnosed according to defined criteria were included in the study.
Interventions: Patients underwent a neurologic evaluation and pedigree charting. Concentric needle EMG was performed on a number of muscles. Motor nerve conduction study of the median, ulnar, and peroneal nerves and sensory conduction study of the median, ulnar, and sural nerves were also performed. Spinal MRI of the cervical region was performed with the 2-T scanner operating at 1.5 T. Gene deletion study of SMN1 and SMN2 was performed in all patients.
Main outcome measures: History of trauma, occupation, exercise, associated medical disease, and cold paresis and muscle wasting, power, reflex changes, and tone.
Results: Fifteen male patients with HD from 14 families participated in the study (mean age at the onset of disease, 18 years; range, 15-23 years). Muscle weakness and wasting were noted in the right upper limb in 12 and the left upper limb in 3, which became bilateral in 8 patients. Cold paresis was present in 6 patients and polyminimyoclonus in all patients. The EMG revealed fibrillations in 10, fasciculations in 15, and neurogenic motor unit potentials in C7, C8, and T1 myotomes in all patients. The EMG abnormalities were unilateral in 5, bilateral in 10, and subclinical in 2 patients. Spinal MRI revealed cord atrophy in 3 of 11 patients. Although family history was present in 1 brother only, the results of both SMN1 and SMN2 gene deletion studies were negative in all patients.
Conclusions: The SMN gene deletion is not found in HD. Exclusive occurrence in male patients and the presence of this disease in 2 brothers suggest a possible role of the X chromosome, which needs further evaluation.