Patterns of Weakness, Classification of Motor Neuron Disease & Clinical Diagnosis of Sporadic ALS

When approaching the patient with suspected motor neuron disease (MND) the pattern of weakness on exam helps distinguish MND from other diseases of peripheral nerves, the neuromuscular junction, or muscle. MND is a clinical diagnosis supported by findings on electrodiagnostic testing, in the absence of other abnormalities on neuroimaging or serological testing. MNDs exist on a spectrum: from a pure lower motor neuron; to mixed upper and lower motor neuron; to a pure upper motor neuron variant in addition to regional variants restricted to the arms, legs or bulbar region. Amyotrophic lateral sclerosis (ALS) is a progressive mixed upper and lower motor neuron disorder, most commonly sporadic (~85%), which is invariably fatal. The only FDA approved treatments for ALS are riluzole, which prolongs life by about 3 months, and dextromethorphan/quinidine which provides symptomatic relief for pseudobulbar affect (inappropriate bouts of laughter or crying). Here we describe a pattern approach to identifying motor neuron disease, and clinical features of sporadic ALS.