Neuromuscular disease in surgical patients can be divided into disorders of the neuromuscular junction, peripheral nerves, and muscle.

Myasthenia gravis

Of all the neuromuscular diseases, myasthenia gravis probably has the most significant implications for surgical patients [1]. This disorder results from an autoimmune attack on the acetylcholine receptors of the postsynaptic (muscle) side of the neuromuscular junction. Characteristic clinical features include fluctuating weakness and fatigue, usually involving the extraocular muscles and eyelids (producing diplopia and ptosis). Weakness of the limbs can be severe, sometimes resulting in almost total paralysis. Sensation and deep tendon reflexes remain intact. Respiratory muscle weakness is common and can be fatal. The introduction of practical mechanical ventilation has resulted in a dramatic decrease in the mortality rate.

Although the clinical features of myasthenia gravis are sufficiently characteristic in some cases, confirmatory tests are usually necessary [2]. The acetylcholine receptor (AchR)- antibody level is elevated in over 80% of patients with myasthenia gravis. Elevated levels of this antibody are extremely specific for this disease [3]. As a result the AchR-antibody serum test is typically the first step in confirming the diagnosis, and the presence of elevated levels eliminates the need for additional confirmatory testing. In antibody-negative patients or when faced with an acutely symptomatic patient, the edrophonium test is often used. Electrodiagnostic studies (repetitive nerve stimulation and single fiber electromyography) are often useful, particularly in antibody-negative patients or patients with cardiac disease or asthma, in whom edrophonium is relatively contraindicated. The characteristic finding on 2- to 3-Hz repetitive motor nerve stimulation is a progressive decrease in the amplitude of the motor response. Single fiber electromyography may reveal the presence of jitter or blocking (a difference in the timing of activation or a failure of neuromuscular transmission in one of a pair of muscle fibers within a motor unit).