October 10, 2019
A 21-year-old man with gradual onset, slowly progressive, spastic weakness of his left upper/lower limbs over the last 2 years. He had a normal lab, workup including CSF, and no sensory deficit or ataxia by neurological examination.
Primary Lateral Sclerosis (PLS) with adaptive compensatory functional changes
- Background
- PLS is a slowly progressive, central motor neuron/tractopathy that can occur at any age. A familial juvenile form may occur in association with ALS2 gene abnormality. It affects either unilateral or bilateral upper motor neurons resulting in normal EMG findings as compared to the fatal Amyotrophic lateral sclerosis (ALS), the latter representing the most common form of motor tractopathy, with similar imaging findings, but different clinical presentation, as it shows both upper motor neuron (UMN) and lower motor neuron (LMN) involvement giving positive EMG findings.
- Key Diagnostic Features
- Atrophy and increased T2/FLAIR signal along the motor cortex and corticospinal tract. A “wide central sulcus” sign helps identify focal volume loss of motor cortical strip. Abnormal iron deposition may give rise to a low signal band on SWI. DTI helps establish the diagnosis by demonstrating fiber loss along the affected corticospinal tract at different levels. BOLD-fMRI findings highlight possible exaggerated response on the affected side due to complex neuroplasticity mechanisms to compensate for chronic neuronal loss.
- Differential Diagnosis
- ALS (gives similar brain imaging findings but clinically affects UMN and LMN).
- Spinal muscular atrophy (Cord findings only and LMN involvement).
- Progressive muscular atrophy (Normal brain/cord MRI and LMN involvement).
- Treatment
- Treatment options include symptomatic therapy for spasticity (Baclofen, Tizanidine), Quinine for muscle cramps, and Diazepam for muscular contractions.
- Additional treatment may include physical, occupational, and speech therapy as well as psychosocial support. Current research groups are studying the role of nerve growth factors, axonal transport, and androgen receptors as future treatment targets.
