In a teleconference you are shown this video of a 65-year-old man with Stage I chronic lymphocytic leukemia and progressive muscle weakness. You are asked to provide a differential diagnosis and give advice as to what tests should be ordered and what treatment should be tried in an attempt to improve his muscular strength.
DIAGNOSIS: Multifocal motor neuropathy (MMN). The clue to the diagnosis in this patient is the occurrence of muscle fasciculations. These can be seen to occur randomly in the pectorals muscles. In contrast to twitches, which usually represent a local irritation, fasciculations are most often a sign of lower motor neuron disease such as might occur in MMN, amyotrophic lateral sclerosis (ALS), and poliomyelitis. Accompanying findings in MNN include muscle weakness and atrophy and diminished reflexes. In ALS, which involves lower motor neurons and the lateral corticospinal tract, one typically finds evidence of both lower and upper motor neuron weakness - the latter characterized by hyperreflexia and increased muscle tone with little atrophy. MMN is usually a paraneoplastic syndrome (as in this case) and may respond to intravenous immunoglobulin therapy.
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