[Primary lateral sclerosis: the era of international diagnosis criteria].

Since Charcot's first description, primary lateral sclerosis (PLS) remains a rare clinical syndrome, a neuropathological phenotype of motor system degeneration. In turn, PLS has been described as belonging to the large spectrum of motoneuron diseases or to the diverse degenerative diseases of the nervous system. Clinically, it is characterized by progressive pyramidal involvement in patients who present insidiously progressive gait disorders and, on examination, have relatively symmetrical lower limb weakness, increased muscle tone, pathologic hyper-reflexia, and exaggerated extensor plantar responses. Pinprick, light touch, and temperature sensations are preserved. Viewed in another way, PLS mimicks progressive hereditary spastic paraparesis (HSP) and the "central" phenotype of amyotrophic lateral sclerosis (ALS). PLS is considered "idiopathic" and, depending on the presence or absence of similarly affected family members, the syndrome of idiopathic HSP and ALS are labeled "hereditary" or "apparently sporadic". The juvenile form of PLS and early age at onset in cases of HSP complicate our understanding of the relationship between these two disorders. Guidelines for diagnosis and genetic counseling have been published for HSP and ALS. Recently, since the first international workshop, guidelines for diagnosis of PLS propose a classification system, e.g. for heterogeneous HSP into "pure PLS", complicated or "plus PLS", symptomatic PLS and upper motor neuron-dominant ALS. However, when reviewing known cases of PLS drawn from the literature, rigorous retrospective application of these new PLS criteria raises an unanswered question: does pure PLS exist?