Isaacs Mertens Syndrome

Rare syndrome with peripheral nerve lesions characterized by muscle stiffness, cramps, and continuous vibrating muscle movements (myokymia).

Hereditary Continuous Muscle Fiber Activity; Isaacs Syndrome.

Autosomal dominant.

Unclear; the role of autoimmunity, specifically antibodies against the potassium channel-inducing hyperexcitability of the peripheral nerve, has been advocated. Probably caused by mutations in the potassium channel gene KCNA1 located on chromosome 12p13.

Characterized by muscular stiffness and cramping, particularly in the limbs with continuous fine, vibrating muscle movements (myokymia).

Neuromuscular signs dominate the disease. Progressive stiffness, cramping, weakness, and constant writhing movements of the muscles under the skin persist during sleep or under general anesthesia without muscle relaxant. Calf hypertrophy can be seen. Electromyography (EMG) shows specific anomalies (spontaneous discharges with rhythmical and continuous firing). Muscle biopsies are abnormal. Clinical examination finds hypertonia, spasticity, speech defect, ataxia, and sometimes seizures. Hyperhidrosis and tachycardia, because of autonomic nervous system involvement, are possible. Association with diaphragmatic hernia has been reported.

Evaluate muscular dysfunction (clinical, EMG), neurologic function (clinical, electroencephalogram (EEG)), and autonomic nervous system involvement (clinical, heart rate variability).

Careful intraoperative positioning is needed. Perioperative blood pressure monitoring is necessary because of autonomic system dysregulation. Regional anesthesia is not contraindicated but probably should be avoided or the benefit must be clearly established because of peripheral nervous lesion (peripheral blocks) and autonomic nervous system involvement (perimedullar blockade).

Consider interaction between antiepileptic treatment and anesthetic drugs. Anesthetic drugs that are suspected to induce dystonia should be used carefully (propofol). Succinylcholine probably should be avoided because of muscular lesion and potential risk of hyperkaliemic response.

Hallervorden-Spatz Disease: Characterized by dystonia (slow, steady muscle contraction distorting limbs, neck, face, mouth, or trunk into certain positions), muscular rigidity, and choreoathetosis. Muscle spasms are present in more than 33% of patients affected with this rare neurologic disorder. Other clinical features seen less often are dysarthria, mental retardation, facial grimacing, dysphasia, muscle atrophy, and seizures.

Hereditary Spastic Paraplegia: Includes weakness, muscle spasms, and stiffness of the legs. Leg muscles may contract or a heel deformity may occur, making walking difficult. Dysphasia, dysphagia, exaggeration of tendon reflexes, and general muscle weakness are symptoms of this autosomal dominant or recessive transmitted disease.

Stiff Man Syndrome (Moersch-Woltman Syndrome): Characterized by progressive rigidity and muscles spasms of the muscles of the neck, trunk, shoulders, and proximal extremities. Caused by abnormal nerve activity most likely in the central, rather than peripheral, nervous system. Electrical activity measured by the EMG may begin in the spinal cord rather than the peripheral nerves.