Violation of neuromuscular transmission

Violation of neuromuscular transmission occurs due to defects of postsynaptic receptors (eg, in myasthenia) or presynaptic release of acetylcholine (eg, botulism), as well as the breakdown of acetylcholine in the synaptic cleft (the action of drugs or neurotoxic drugs). Typical fluctuations in the degree of muscle weakness and fatigue.

Diseases in which there is a violation of neuromuscular transmission

Eaton-Lambert syndrome develops when the release of acetylcholine from the presynaptic nerve endings is impaired.

Botulism is a consequence of the disruption of the release of acetylcholine by the presynaptic terminal due to the irreversible binding of the toxin Clostridium botulinum. Symptoms include severe weakness up to breathing disorders and signs of an increase in sympathetic tone due to blocking of parasympathetic activity: mydriasis, dry mouth, constipation, urinary retention, tachycardia, which is not the case with myasthenia gravis. On EMG, a moderate decrease in the response to a low-frequency (2-3 in 1 second) nerve irritation and an increase in response with an increase in the frequency of stimulation (50 imp / s) or after a brief (10 s) muscular work.

Drugs or toxic substances can disrupt the function of the neuromuscular synapse. Cholinergic drugs, organophosphate insecticides and most of the neuromuscular gases block neuromuscular transmission, depolarizing the postsynaptic membrane due to the excessive action of acetylcholine on its receptors. Result: miosis, bronchorrhea, myasthenopodobnaya weakness. Aminoglycosides and polypeptide antibiotics reduce the presynaptic release of acetylcholine and the sensitivity of the postsynaptic membrane to it. Against the background of latent myasthenia gravis, high concentrations of these antibiotics in the serum exacerbate the neuromuscular block.

Long-term treatment with penicillamine may be accompanied by a reversible syndrome, which clinically and according to EMG resembles myasthenia gravis. Excess magnesium (a blood level of 8-9 mg / dL) is fraught with the development of severe weakness, which also resembles the myasthenic syndrome. Treatment includes the elimination of toxic effects, intensive monitoring and, if necessary, mechanical ventilation. To reduce the excess bronchial secretion, atropine is prescribed 0.4-0.6 mg orally 3 times / day. When poisoning with organophosphorous insecticides or nerve gas may require higher doses (2-4 mg IV in 5 minutes).

The syndrome of a rigid person is a sudden appearance of progressive rigidity of the muscles of the trunk and abdomen, to a lesser degree of limbs. There are no other abnormalities, including EMG. This autoimmune syndrome develops as paraneoplastic (more often with cancer of the chest, lungs, rectum and Hodgkin's disease). Autoantibodies against several proteins associated with GABA glycine synapses, mainly affect the inhibitory neurons of the anterior horns of the spinal cord. Treatment is symptomatic. Diazepam significantly reduces muscle rigidity. The results of plasmapheresis are contradictory.

The syndrome of Isaacs (synonyms: neyromiotonia, battleship syndrome) is manifested mainly by complaints about the work of the limbs. There are myoquima - muscle fascination, which looks like a conglomerate of worms moving under the skin. Other complaints: carpopedic spasms, intermittent cramps, increased sweating and pseudomotonia (impaired relaxation after a strong muscle contraction, but without a typical increase in myotonia - decrease in EMG). Initially affects the peripheral nerve, as curare removes complaints, and under general anesthesia the symptoms persist. The reason is unknown. Carbamazepine or phenytoin reduce complaints.

[1], [2],