Primary Lateral Sclerosis
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- Primary lateral sclerosis (PLS) is a rare progressive degenerative disease of the corticospinal and corticobulbar tracts (upper motor neurons [UMNs]), which spares the anterior horn cells.
- Characterized by leg weakness, spasticity, and bulbar symptoms like dysphagia and dysarthria
- Additional features include cognitive impairment, eye movement abnormalities, and urinary dysfunction.
- Part of the spectrum of motor neuron diseases (MNDs) because some patients with PLS evolve to develop amyotrophic lateral sclerosis (ALS)
- Conversion from PLS to ALS has been reported up to 27 years after the onset of spasticity.
- Found in 1–3% of patients with motor neuron disorder
- Onset is usually after age 40 years, although a juvenile form has been described.
- Mean age at symptom onset is 54 years.
- There is a slight male predominance, which is similar to ALS.
Incidence is difficult to determine due to rarity, misdiagnosis, and changing diagnosis. An estimated 1/10 million/year or 300 to 500 people in the United States are diagnosed yearly.
Estimated prevalence is 10 to 20/million.
Etiology and Pathophysiology
PLS is usually sporadic with no known cause; potential role of TAR DNA–binding protein 43 (TDP-43) (1)
- Juvenile PLS and juvenile ALS has been correlated with a mutation in the ALS2 gene on chromosome 2. It is inherited in an autosomal recessive pattern.
- Mutation of the ERLIN2 gene, a component of the endoplasmic reticulum lipid raft has been linked to juvenile PLS.
There is no known means of prevention.