Neuromuscular transmission disorders

Pain, muscular weakness, cramps and ease of fatigue are the most usual symptoms of muscular disease. In most cases, it is diseases of the vascular or nervous system or problems with the processes providing energy within the muscle that are responsible for clinical problems with muscles. Other clinical problems include the muscular dystrophies, myotonic disorders, inflammatory myopathies and disorders of neuromuscular transmission (see Walton, 1996). The best known is Duchenne muscular dystrophy. 

Myasthenia gravis is an autoimmune disease resulting from production of autoantibodies against AChR at the motor end plate, causing defects in neuromuscular transmission. Depending on the muscles affected a patient may develop dysphagia or respiratory failure [1]. The appearance of pathological forms of erythrocytes such as stomatocytes, echinocytes etc., in peripheral blood causes microcirculation disorders [2]. 

In the presence of nenromnscnlar disorders, such as myasthenia gravis or Lambert-Eaton sjmdrome, botulinum toxin-induced inhibition of acetylcholine release can cause generalized weakness (17). Therefore, botulinum toxin should, if at aU, be used with extreme caution in patients with neuromuscular disease, who have a reduced margin of safety with regard to neuromuscular transmission. 

While the exact cause of muscle weakness was unclear, this case argues against the use of botulinum toxin in patients with myasthenic syndromes. When the margin of safety is reduced with regard to neuromuscular transmission, botulinum toxin can result in increased morbidity or even mortality. Generalized muscle weakness after botulinum toxin has also been reported in patients with other neuromuscular disorders (18). In addition, it should be remembered that both dysphagia and muscle weakness can occur after botulinum toxin injection, even in patients who do not suffer from generalized neuromuscular disorders (19). 

The skeletal muscle ma5 be relaxed by two different groups of drugs, namely first, by those exerting an aetion on the central nervous system (CNS) and used mainly for the relief of painful muscle spasms of spasticity taking place either in neuromuseular or musculoskeletal disorders secondly, those aflfeeting neuromuscular transmission that are employed as adjrmcts in anaesthesia in order to modify the musele relaxation ability. 

Table 2 summarize.s the main clinical and EMG characteristics of some well-known disorders of neuromuscular transmission. Myasthenia gravi.s i.s an autoimmune disorder with postsynaptic impairment of neuromu.scuiar transmission due to complement deposition at the ACh receptor... 

TABLE 2. Main Characteristics of Some Human Disorders of Neuromuscular Transmission... 

The eyelid disorders may be related not only to neuromuscular transmission, as in myasthenia gravis, but also to intrinsic muscle weakness and cranial neuropathy. 

Vincent A, Beeson D, Lang B. Molecular targets for autoimmune and genetic disorders of neuromuscular transmission. Eur J Biochem 2000 267(23) 6717-28. 

CNS). Pyridostigmine has been used for many years in the therapy of neurological disorders, especially myasthenia gravis, a disease of neuromuscular transmission. In patients with myasthenia gravis, inhibition of synaptic AChE is clinically beneficial. 

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