Neuromyotonia

05 November 2004 

Syndrome of continuous and spontaneous muscular activity

Undulating myokymia, syndrome of continuous muscle fibre activity, Isaac’s syndrome, neurotonia, idiopathic generalized myokymia.

ACQUIRED

Idiopathic

Associated with autoimmune disorders

            Thymoma+/- myasthenia gravis

            Bronchial tumors +/- neuropathy

            Myasthenia gravis

            Neuropathies

            Penicillamine

Toxic neuropathies: insecticide, herbicide, alcohol, toluene, gold

INHERITED

Episodic ataxia

Hereditary motor or sensorimotor neuropathy

Schwartz-Jampel syndrome

Distal spinal muscular atrophy

CLINICAL

Generalized stiffness, cramps, myokymia

Weakness

Pseudomyotonia

Pseudotetany with Chvostek & Trousseau

Percussion myotonia rare

INVESTIGATIONS

CSF: normal cell counts & protein

Muscle biopsy not useful

Skin biopsy not useful

EMG: muscle overactivity abolished by blockade of NMJ by curare or succinylcholine

            Fibrillations, fasciculations

            Neuromyotonia:            spontaneous motor fibre discharges occurring in distinctive

doublets, triplets up to several seconds

high 40-300 Hz intraburst frequency

occur at irregular intervals of 1-30 sec

NCS:   1/3 show some evidence of neuropathy

Antigen in neuromyotonia presumed neuronal Shaker related voltage gated potassium channel

TREATMENT

Symptoms:       Tegretol 200-600 mg/d or dilantin

                        Epilim, dantrolene, diazepam

Plasma exchange

Intragam rarely