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Science News: Primary Lateral Sclerosis: Consensus Diagnostic Criteria

Submitted and Edited by Francisco Gomez, MD

Primary lateral sclerosis: consensus diagnostic criteria. Turner MR, Barohn RJ, Corcia P, et al. Journal of Neurology, Neurosurgery & Psychiatry. Published Online First: 06 February 2020. doi: 10.1136/jnnp-2019-322541

Primary Lateral Sclerosis (PLS) is a neurodegenerative disease affecting upper motor neurons primarily. This disease tends to affect around age 50, initiating with gait difficulties progressing to spastic paraparesis. Other initial symptoms may include corticobulbar dysfunction, cognitive dysfunction or pseudobulbar affect as well as urinary symptoms. Cognitive function loss, and especially signs of frontotemporal dementia may be less frequently observed, as compared to ALS.

Diagnosis may prove challenging as PLS can closely mimic Ammyotrophic Lateral Sclerosis or Hereditary Spastic Paraparesis and there is no clear histopathological distinction between PLS and the ALS in and there is controversy about whether these two diseases are part of a  common pathological continuum. A delay to diagnosis is commonly observed, as previous criteria required a disease progression of 3-5 years.

Age >25 years and the presence of: progressive upper motor neuron (UMN) dysfunction for a minimum of 2 years  in at least 2 out of 3 regions: lower extremity, upper extremity, bulbar. The absence of sensory symptoms, signs of active lower motor neuron  degeneration†, no alternative diagnosis.Under the proposed criteria, Probable PLS is defined by the absence of significant active LMN degeneration at 2–4 years from symptomatic debut, and Definite PLS is defined by the absence of significant active LMN degeneration 4 or more years from onset.

Comments: The authors also offer a tour de force on emergent diagnostic technologies in the diagnosis if PLS. Transcranial Magnetic Stimulation demonstrate longer conduction times and decreased cortical excitability in PLS, differentiating this entitity from PLS and Hereditary Spastic Parapareis, respectively. As neurofilaments have emerged as a biomarker of neuronal degeneration, PLS has exhibited less levels of these markers, as compared to ALS. The authors further described emerging MRI  volume quantifying technology as a method to better detect PLS mediated prefrontal gyrus degeneration.

While PLS is a relatively rare disease, simplified diagnostic criteria permitting earlier diagnosis of a disease which is so similar clinically to other entities is a boon to both clinicians and patients anxious for a diagnosis. They may also decrease practice variation and may aid in the recognition of this disease however, they remained to be verified in real world application.

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