Hirayama's disease, also referred to as Monomelic amyotrophy, MMS, Sobue disease, or Juvenile non-progressive amyotrophy, is an un-treatable, focal, lower motor neuron disease. Hirayama's disease affects mainly younger males who are between the ages of fifteen and twenty-five years of age, mostly in the nations of India and Japan. Hirayama's disease is characterized by the insidious onset of muscular atrophy.
The muscular atrophy associated with Hirayama's disease stabilizes at a plateau of between two and five years. After this period of time, the muscular atrophy does not improve; however, it does not worsen either. People with Hirayama's disease do not experience pain or sensory loss because of the disease. Unlike other forms of lower motor neuron diseases, Hirayama's disease is not one that is believed to be hereditary. For people who have this disease, 'fasciculations,' or involuntary muscle twitches, are rare.
Hirayama's disease is much less common in North America. Both the onset of the disease, as well as the progression of it, are slow. For the majority of people with the disease the cause remains unknown, although there have been some reports published that have linked Hirayama's disease to either radiation or traumatic injuries. Familial forms of the disease also exist.
Hirayama's disease is characterized by a progressive degeneration and loss of motor neurons. Motor neurons are the nerve cells in a person's spinal cord and brain that are responsible for controlling their voluntary muscle groups. The disease is also characterized by the wasting and weakening of a single one of a person's limbs. The limb affected is usually a hand or an arm, instead of a leg or foot. While the person affected by Hirayama's disease does not experience any pain in association with the disease, there are doctors who contend that the person can experience a mild sensory loss in association with the disease. A number of experts have suggested that sensory loss symptoms may actually indicate a cause other than Hirayama's disease.
The symptoms of Hirayama's disease as a whole, like the muscular atrophy associated with the disease, progress for a period of time, reaching a plateau, and then remain stable for many years after that point. The person affected by the disease experiences a certain level of disability due to the disease. On rare occasion, the weakness associated with Hirayama's disease may progress to the person's opposite limb. There is also a progressive variant of the disease that is referred to as, 'O'Sullivan-McLeod Syndrome,' which affects only the small muscles of a person's hand and forearm. O'Sullivan-McLeod syndrome also has a course that progresses slowly.
The signs and symptoms of Hirayama's disease can include:
A diagnosis of Hirayama's disease is made through a physical examination of the affected person and their medical history. Use of electromyography (EMG), a type of special recording technique that detects electrical activity in a person's muscles, may show a loss in their nerve supply or, 'denervation,' in the limb that is affected. A doctor may order Magnetic Resonance Imaging (MRI) or Computerized Tomography (CT) scans to show any muscle atrophy. People who are believed to have Hirayama's disease should be followed by a neuromuscular disease specialist for several months to ensure that there are no signs of any other forms of motor neuron disease or their development.
EMG testing can reveal denervation in the limb of a person affected by Hirayama's disease, but it may also show signs of, 'reinnervation,' in the person's limb, or whether the person's limb has a conduction block. People with the disease may experience coldness, sweating, or cyanosis, according to reports by some people with Hirayama's disease. Their reports indicate involvement of their sympathetic nervous system.
Medical science has not found a cure for Hirayama's disease at this time. The forms of treatment approaches common to this disease include muscle strengthening exercises, as well as training related to the person's hand coordination.