Primary Lateral Sclerosis (PLS)

What Is Primary Lateral Sclerosis?

As a class of neurodegenerative disorders, motor neuron diseases are a heterogeneous group of conditions caused by the degeneration or and death of the neurons selectively controlling voluntary muscle movement. According to the affected motor neurons, two of these motor neuron diseases are distinguished, which are amyotrophic lateral sclerosis (ALS) affecting both the upper motor neurons and the lower motor neurons, and primary lateral sclerosis (PLS) only affecting the upper motor neurons. Accordingly, PLS is a rare progressive and degenerative disease characterized by upper motor neuron dysfunctions as well as spinal cord and medulla oblongata paralysis. The clinical symptoms of PLS are usually manifested as limb rigidity, hyperreflexia, progressive muscle weakness, muscle atrophy and fascicular fibrillation, spasticity, and so forth.

Causes and Diagnosis of Primary Lateral Sclerosis

Although PLS is a nonfamilial neurodegenerative disorder that affects both males and females over 50 years old, it also has been reported that affects children. Juvenile PLS is an autosomal recessive inherited disease caused by mutations in the ALS2 gene. The exact cause of the adult-onset PLS is still not so clear. But, the environmental factors, aging, local brain trauma, inheritance, demyelinating diseases, etc., all are possible causes of PLS.

The diagnosis of PLS is challenging since it may present symptoms signs like other neurological diseases, such as ALS and hereditary spastic paraplegias. And, unlike ALS where multiple proposed biomarkers have been identified, no validated biomarker has been published up to now. 43-kDa transactive response DNA-binding protein (TDP-43) once has been identified as the major pathological protein of ALS, which also was employed for neuropathological characterization but not for clinical diagnosis. Therefore, the current diagnosis of PLS mainly relies on upper motor neuron dysfunction examination after exclusion of other possible causes of the symptoms.

Fig.2 Diffusion tensor imaging and fluorodeoxyglucose positron emission tomography findings in PLS. (Turner, 2020)

Treatment of Primary Lateral Sclerosis

Currently, no effective treatment has been developed to cure, prevent, or reverse the PLS. Common therapies are aiming to alleviate symptoms and improve functioning. The treatment strategies include non-medication physical therapy and medication treatment. Physical exercise is beneficial to maintain muscle strength, flexibility, reduce muscle spasticity, and prevent joint immobility. For medication treatment, baclofen, tizanidine, and valium are the first choice for the relief of spasticity. For patients with spasticity that cannot be administered orally, surgically implanting a baclofen pump is recommended. Anticholinergic drugs, such as atropine and glycopyrrolate are common utilized to manage excess oral secretions or drooling.

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Reference

1. Turner, M.R.; et al. Primary lateral sclerosis: consensus diagnostic criteria. Journal of Neurology, Neurosurgery & Psychiatry. 2020, 91(4): 373-377.