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Primary Lateral Sclerosis (PLS)

A 62 year-old woman presented with progressive weakness over two years. Her examination spasticity and increased reflexes in all four limbs. Both planter responses were extensor. Otherwise, mental state, sensation and the remainder of the neurology exam was normal.

Axial MRI scan (Flair Image): Note the well demarked areas (arrows) of increased signal that correspond to the location of the corticospinal tracts. Primary Lateral Sclerosis is an atypical variant of motor neuron disease. As opposed to Amyotrophic Lateral Sclerosis (ALS) that affects both lower and upper motor neurons, in PLS, abnormalities are restricted to the upper motor neuron. In some cases, upper motor neuron degeneration can be seen on MRI scans, especially Flair imaging.

Revised 06/10/04.
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