What’s in a name?

The diagnostic challenges in motor neuron disease are deceptively simple. A definitive diagnosis of amyotrophic lateral sclerosis (ALS) requires a combination of progressive upper and lower motor neuron features.¹ The diagnostic label of primary lateral sclerosis (PLS) describes patients with exclusively upper motor neuron signs while progressive muscular atrophy (PMA) describes those with only lower motor neuron involvement.² Although these diagnostic labels suggest a match to affected populations of motor neurons, there are few, if any, other neurodegenerative diseases where the phenotypic expression of the disease varies as markedly as that observed in the spectrum of ALS and the related motor neuron disorders.³ Clinical and pathologic features beyond the motor system are almost universal in all the clinical forms of the disease. The obstacles we currently confront in assigning the few available diagnostic labels to identify individual disease entities within the large spectrum of motor neuron disease may be the most serious impediment to our understanding and treatment of these diseases. On the other hand, these clinical phenotypes are well known, may be easily recognizable, and are hallowed in the history of …