• A 16-year-old boy was seen for severe episodic muscle cramps and generalized myokymia, consistent with Isaacs's syndrome. Bilateral calf hypertrophy (46-cm calf circumference) and ankle areflexia were noted. He was treated with phenytoin sodium, 300 mg/ day. Within three months there was marked decrease in myokymia, total relief of cramps, return of ankle reflexes, and 6-cm reduction in calf circumference. We suggest that the excess muscle activity in Isaacs's syndrome may be responsible for the associated phenomena of muscle hypertrophy and areflexia.
Zisfein J, Sivak M, Aron AM, Bender AN. Isaacs' Syndrome With Muscle Hypertrophy Reversed by Phenytoin Therapy. Arch Neurol. 1983;40(4):241–242. doi:10.1001/archneur.1983.04050040071012