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Patients with PLS occasionally have mild, nonspecific, and nonprogressive findings of denervation on electrodiagnostic testing. The severity of the denervation and reinnervation does not resemble that seen in ALS and does not justify these patients' being classified as having ALS. These patients may be concerned that their PLS eventually could evolve into ALS. Although absolute guarantees cannot be given, some measure of reassurance may be derived from the overall slow progression in these patients.
As overall activity diminishes, muscle atrophy may suggest lower motor neuron involvement. Such changes may be distinguished from muscle atrophy due to disuse secondary to upper motor neuron impairment on clinical grounds (eg, no fasciculations) and, more definitively, by electrophysiologic testing. Occasionally, sparse, scattered, nonprogressive changes of denervation (ie, fibrillation potentials) may be seen in distal muscles