Neuromyotonia (Isaacs Syndrome) may occur as a paraneoplastic syndrome. The neurological findings may appear months or years before the tumor is identified.


Clinical features of neuromyotonia:

(1) muscle twitching

(2) muscle cramps

(3) muscle stiffness and delayed relaxation

(4) muscle weakness

(5) transient paresthesias

(6) variable axonal polyneuropathy


Laboratory findings may include:

(1) motor nerve hyperexcitability on electrophysiologic studies with repetitive compound muscle action potentials (CMAP) afterdischarges, fasciculations and neuromyotonic discharges

(2) variable presence of antibodies to VGKC (voltage-gated potassium channel)


Tumors reported to cause a paraneoplastic neuromyotonia:

(1) lung cancer

(2) thymoma

(3) Hodgkin's disease

(4) plasmacytoma

(5) renal cell carcinoma

(6) urinary bladder carcinoma

(7) ovarian cancer


Diagnosis as a paraneoplastic syndrome:

(1) acquired disorder (not hereditary)

(2) presence of a tumor

(3) exclusion of other causes

(4) disease activity related to amount of tumor present


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