Clinical, Electrodiagnostic, Sonographic, and Radiological Findings of Hirayama Disease: A Report of Two Cases and a Review of the Literature.

Hirayama disease (HD) is a rare disorder characterized by insidious asymmetric neurogenic atrophy primarily involving the upper extremities. HD most commonly affects adolescent males and has a favorable prognosis for arrest of progression. Electrodiagnostic (EDX) studies show chronic denervation changes in the distal upper extremity muscles. A cervical spine MRI in neck flexion may reveal compression of the cervical ventral spinal cord. We report clinical, EDX, and MRI findings in two cases of HD. The first case involved a 15-year-old male with a six-month history of progressive weakness, wasting, and tremulous movements of the left hand without pain or paresthesia. A physical exam revealed marked wasting of the left intrinsic hand muscles with polyminimyoclonus. Needle electromyography (EMG) revealed fasciculations (simultaneous with the polyminimyoclonus) while at rest and recruitment of 1-2 large polyphasic units in the left C8, T1, and, to a lesser extent, the C7 distribution. A T2-weighted flexion cervical spine MRI revealed narrowing and anterior displacement of the posterior dura of the cervical cord, leading to cord compression at C5-6 and C6-7. At last contact 11 years following symptom initiation, the patient continued to complain of profound weakness of the left hand without pain or numbness. The second case involved a 17-year-old male who was found to have wasting of the intrinsic muscles of the non-dominant left hand on a routine physical examination. The left first dorsal interosseus, abductor digiti minimi, abductor pollicis brevis, and extensor pollicis longus muscles were found to be clinically weak. Polyminimyoclonus involving all fingers of the left hand was also observed. A needle EMG demonstrated fasciculations with large amplitudes and wide duration motor unit potentials in the left C8, T1, and, to a lesser extent, C7 distribution. An ultrasound study showed frequent fasciculations in the left intrinsic hand muscles and the distal forearm muscles simultaneously with the polyminimyoclonus. A T2-weighted cervical spine MRI scan in the flexed sagittal position revealed anterior displacement of the dura and an enlarged epidural space from C4-C7. At last follow-up 11 months later, the findings were unchanged. The EDX studies and cervical MRI findings were consistent with HD in both cases. The role of EDX studies and cervical spine flexion MRI in diagnosing HD and the correlation between polyminimyoclonus and fasciculations are highlighted.