Is there a diagnosis of Hirayama disease
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The prevalence is unknown. The disease is seen mainly in Asian countries (mostly Japan and India), with very few cases reported from Europe and the United States. A nationwide survey in Japan from 1996 to 1998 identified 333 cases, corresponding to a prevalence of about 1 / 33,300.
MA is seen more often in males (male / female = 20: 1) with an onset of the disease in the 2nd to 3rd decade of life (ages 14-25). Muscle weakness and wasting begins in the hand or forearm on one side. Muscle atrophy is not associated with pain or sensory changes. The disease is slowly progressive, usually over 3-9 years. Then the symptoms stop and stabilize. Occasionally, after the age of 40, the disease becomes unstable and progresses again. In rare cases, the disease spreads to the other limb. Other rare signs are: worsening of symptoms with exposure to cold (cold paralysis), muscle cramps, cold hands, irregular gross tremor and / or contraction fasciculation. O'Sullivan-McLeod syndrome (see there), which is believed to be a variant of MA, presents with weakness of the intrinsic hand muscles. It starts unilaterally, but can progress to the other limb with asymmetrical distribution.
The exact etiology is not known. One theory states that the cause of MA is a forward displacement of the cervical dura, caused by repeated flexion of the neck with compression of the anterior part of the spinal cord against the anterior edge of the vertebral body. Autoimmunity, toxins, and infections have also been identified as possible causes, but more evidence is needed. As several familial cases of MA have been described (
Diagnosis is based on findings from clinical imaging and electromyography. With magnetic resonance imaging (MRI), a characteristic finding is made: When the patient has maximally anteflexed the neck, the anterior horn appears compressed (snake eye sign). The atrophy in the lower cervical spinal cord can also be seen. The investigation of the nerve conduction velocity reveals a reduced compound muscle action potential of the median and ulnar nerves of the affected limb. F-wave examinations show a reduced frequency and an increased minimum latency in these muscles.
Poliomyelitis, multifocal motor neuropathy with conduction block, syringomyelia (see these terms), anterior interosseous or deep ulnar neuropathy, cervical vertebra anomalies, spinal cord tumors, brachial plexopathy and trauma must be excluded.
Management and treatment
The MA cannot be cured. Treatment is conservative and, if diagnosed early, aims to slow the progression of muscular atrophy. Wearing a ruff in the early stages of the disease has in some cases stopped the progression by preventing the neck from flexing. Exercises to strengthen muscle strength and to coordinate the hands have also proven helpful.
MA is not life threatening, but it can cause social problems in patients with complete loss of hand function. Early intervention is appropriate to minimize the progression of the disease.
Reviewer: Dr Satoshi KUWABARA - Last update: October 2012
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