Cause
The disability originates with impaired functioning of the anterior horn cells of the lower cervical cord (lower neck), but the cause of the decline is not fully understood and is still considered unknown. Researchers, including Hirayama, believe that "forward displacement of the cervical dural sac and compressive flattening of the lower cervical cord during neck flexion" is the contributing factor. Studies consistently note a loss of normal neck curvature (the cervical lordosis) and compression of the cervical chord by the dural sac in forward flexion. "There is a debate about whether this condition represents a focal form of primary LMN degeneration (ie, a focal form of spinal muscular atrophy) or a local consequence of chronic compression from a dural expansion in the cervical spine. "A familial link has been found in a minor percentage of cases, including parent-child and sibling-sibling. Because of the unusual distribution of the disease, some researchers speculate that there could be an ethnic link. Diagnosis
The condition presents almost exclusively in 15- to 25-year-old adults experiencing weakness in hand and arm. A patient history and a neurological exam narrows down the possible diagnosis; this preliminary exam typically includes strength and reflex tests. Cold paresis (increased weakness in cold weather) is reported by most patients (> 80%). Fasciculations are reported as uncommon (< 20%) to common; larger tremors  are more consistently cited. Males are far more likely to be diagnosed with the condition.The disease is rare and several cited cases deviate from the expected norm, making diagnosis more difficult.
Pain and tingling in the hand is typically present in CTS and absent from MMA; loss of function presents differently; with careful electrophysiological study and neurological exams the two are distinguished. In early stages, ALS, SCA, and MMA, presentation may be similar. Both CSA and ALS ultimately have more extensive symptoms. MMA is more prevalent in young people while ALS and CSA are more common in older populations. With ALS, hand symptoms usually more commonly both proximal and distal vs in MMA mostly distal only, and with ALS fasciculations (twitching) are often present in upper extremities, but rarely in MMA. MMA is usually eliminated from consideration if disability expresses itself in more than one extremity or in lower extremities (legs), but symptomatic absence may not rule out ALS for three to five years after initial onset. Electrophysiological texts and reflex tests tend to yield different results, but interpretation is at times subjective. Treatment
At present there is no cure for MMA. The impact on the affected individual ranges from minimal to significant depending on the extent of the weakness. Physical and occupational therapies include muscle strengthening exercises and training in hand coordination. Early use of a cervical collar is increasingly encouraged as therapeutic for arresting further compression of the cervical spinal cord. Spinal surgery on patients with more advanced symptoms has met with reported success, but is still regarded as experimental. Prognosis
The symptoms of MMA usually progress slowly for two to five years and then remain stable for many years.