Congenital myasthenic syndromes

Congenital myasthenic syndromes

Anesthetic relevance
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Signs and symptoms
Diagnosis
Treatment
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Congenital myasthenic syndromes (CMS) are a genotypically and phenotypically heterogeneous group of rare neuromuscular disorders that cause impaired neuromuscular transmission. Inheritance can be autosomal dominant or recessive.

Anesthetic implications

Preoperative optimization

Preop evaluation may involve planning with a neurologist and geneticist to determine the patient's subtype and what medications may be effective.

Pathophysiology

Caused by mutations for proteins involved in neuromuscular transmission (organization, maintenance, function or modification of motor endplate). These mutations result in either gain or loss of function causing a change in the magnitude of the response to acetylcholine. Subtypes are classified based on where the defect occurs: presynaptic, synaptic, and postsynaptic. The most common type is post-synaptic, secondary to a mutation in synaptic vesicles, acetylcholinesterase, or nicotinic acetylcholine receptors.

These differ from myasthenia gravis and Lambert-Eaton, which are mediated by autoantibodies.

Signs and symptoms

Signs: ophthalmoplegia, ptosis, dysphonia, swallowing disturbance, facial paresis, muscle fatigability, recurrent apnea

Acute respiratory failure may occur triggered by infections episodes

Diagnosis

Tensilon test (EMG with repetitive nerve stimulation), muscle biopsy, genetic analysis may be used to confirm diagnosis.

Treatment

Medication

Administration of medication without knowing subtype of CMS is unadvised.

Acetylcholinesterase inhibitors are most frequently used, if the subtype is appropriate. 4-diaminopyridine is an alternative, which increases amount of acetylcholine released in the synaptic cleft.

Other medications that may be used include salbutamol, albuterol, ephedrine, fluoxetine, and other experimental choices.

Nonmedical therapy

Physiotherapy, speech and occupational therapy, invasive treatment such as feeding tubes and mechanical ventilation may be required.

Unlike in Myasthenia Gravis, plasmapheresis is not effective as the pathology is not due to antibodies.

Prognosis

Pregnancy has been reported to exacerbate clinical symptoms.

Epidemiology

Estimated 1:500,000 prevalence