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. Proposed diagnostic criteria: # Distal predominant muscle weakness and atrophy in forearm and hand # Involvement of the unilateral upper extremity almost always all the time # Onset between the ages of 10 to early 20s # Insidious onset with gradual progression for the first several years, followed by stabilization # No lower extremity involvement # No sensory disturbance and tendon reflex abnormalities # Exclusion of other diseases (e.g., motor neuron disease, multifocal motor neuropathy, brachial plexopathy, spinal cord tumors, syringomyelia, cervical vertebral abnormalities, anterior interosseous, or deep ulnar neuropathy) MRI A neurological exam can suggest different motor neuron diseases (such as MMA), but to more confidently distinguish MMA from the diseases it mimics, advanced diagnostic tools are called for. These include exam tools such as Magnetic resonance imaging (MRI), and electromyography (EMG) and nerve conduction velocity (NCV) tests. An MRI examination of the neck would typically reveal - for a positive MMA diagnosis—some constriction of the cervical cord and an abnormal forward extension of the neck, ("loss of cervical lordosis"); pressure by the dura on the nerve cord apparently causes the flattening / narrowing. An EMG test reveals loss of the nerve supply, or denervation, in the affected limb without a conduction block (a nerve blockage restricted to a small segment of the nerve). In early stages of the disease MMA may be confused for amyotrophic lateral sclerosis (ALS), cervical spondylotic amyotrophy (CSA), and other challenging neurological diseases, as well as conditions that are minor but that call for very different treatments, such as advanced carpal tunnel syndrome (CTS). Symptoms somewhat differ. 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.
Monomelic amyotrophy
Congenital distal spinal muscular atrophy
Chondrodystrophy
Spinal muscular atrophy with lower extremity predominance 1
Hereditary neuralgic amyotrophy
Spinal muscular atrophy
Congenital muscular dystrophy
Spinal and bulbar muscular atrophy