Feline Myasthenia Gravis Study Guide

Overview and Clinical Importance

Myasthenia gravis (MG) is an autoimmune neuromuscular disorder characterized by the production of autoantibodies against acetylcholine receptors (AChRs) at the neuromuscular junction (NMJ). In cats, MG is relatively uncommon compared to dogs but represents a clinically significant cause of generalized muscle weakness and regurgitation. Understanding this condition is essential for NAVLE preparation as it tests knowledge of neuromuscular physiology, autoimmune pathology, and clinical medicine.

Feline MG differs from canine MG in several important ways: cats have a higher association with thymoma (52% vs 3-4% in dogs), a lower incidence of megaesophagus (60% vs 84% in dogs), and rarely achieve spontaneous remission (9.2% vs 88.7% in dogs). Abyssinian and Somali cats have an increased predisposition to the disease.

Pathophysiology

Normal Neuromuscular Transmission

Normal neuromuscular transmission involves the release of acetylcholine (ACh) from the presynaptic motor neuron terminal into the synaptic cleft. ACh binds to nicotinic acetylcholine receptors (nAChRs) on the postsynaptic motor end plate, causing ligand-gated ion channels to open. This allows sodium influx and generates an end-plate potential (EPP), which triggers muscle fiber depolarization and contraction. The enzyme acetylcholinesterase (AChE) rapidly degrades ACh in the synaptic cleft to terminate the signal.