How is primary lateral sclerosis (PLS) differentiated from amyotrophic lateral sclerosis (ALS)?

Updated: Sep 06, 2019
  • Author: Carmel Armon, MD, MSc, MHS; Chief Editor: Nicholas Lorenzo, MD, MHCM, CPE, FAAPL  more...
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ALS may present initially with signs of only upper or lower motor neuron involvement. Thus, a process that initially is considered PMA or PLS has the potential to be reclassified as ALS if sufficient signs of a combination of upper and lower motor neuron involvement develop over time. In some cases, such reclassification may occur only at autopsy (eg, if pyramidal tract involvement is found in patients who did not have signs of upper motor neuron involvement during life and whose disease was therefore classified on clinical grounds as PMA). (See History, Physical Examination, and Differentials.)

Reports have described patients with 1 of the genes for familial ALS in whom only lower motor neuron involvement was seen during life and at autopsy. Most investigators would classify this disease pattern as ALS on the basis of the gene's presence (even though its clinical expression was incomplete). This position is supported by the World Federation of Neurology diagnostic criteria for ALS.

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