QUARTERLY BEAT
OCTOBER 2026
WEBINAR HIGHLIGHTS
MYASTHENIA GRAVIS
Missy Carpentier, DVM, DACVIM (Neurology) Minnesota Veterinary Neurology, Columbus, MN
What do you do when weakness, regurgitation, or megaesophagus has you wondering whether myasthenia gravis could be the culprit? In this VETgirl article Dr. Missy Carpentier, DACVIM (Neurology), expands on myasthenia gravis, an important differential diagnosis covered in her October 15, 2025 VETgirl webinar, The Acute Lower Motor Neuron Canine . Read on for practical guidance on recognizing clinical presentations in dogs and cats, confirming the diagnosis, selecting treatment options, and managing complications like aspiration pneumonia to help support these patients through treatment and recovery. Want to learn more? Check out the on-demand webinar HERE !
Myasthenia Gravis (MG) can be both congenital and, more commonly, acquired with the dominating clinical sign being weakness. Dogs with the congenital form of the disease present at less than a couple months of age and have abnormal development of the acetylcholine receptors. The congenital form is rare. We are going to focus on the acquired form of the disease in this article, but if you have a juvenile patient who you suspect has MG, remember that there is a congenital form and they will not test positive on the acetylcholine receptor-antibody (AChR-Ab) test because they do not have autoantibodies against the receptor. ACQUIRED MG Acquired MG is a disease in which autoantibodies are directed against acetylcholine (Ach) receptors on the postsynaptic membrane on the neuromuscular junction. S
FELINE PRESENTATIONS In cats, the most common clinical presentation is generalized weakness, reported as the main clinical sign in 54.3% of cases. 2 They can also present with megaesophagus or dysphagia, in addition to generalized weakness. Cats are much less likely to present with focal MG, where clinical signs are localized to the esophagus or pharynx only, mainly due to the fact that the feline esophagus is a combination of skeletal and smooth muscle versus the canine esophagus that is entirely skeletal muscle. Unlike in dogs, in which only 3.4% present with a mediastinal mass, 25.7-52% of cats will present with a mediastinal mass that is most often a thymoma. 2-4 MG presents with a greater incidence in Abyssinian and Somali cats. 2, 4 An adverse drug reaction to methimazole is another cause of acquired MG in cats.
CANINE PRESENTATIONS
DIAGNOSIS
There are three classic forms for acquired MG in canines and they include: • Focal MG: Predominant pathology is megaesophagus and, therefore, the classic clinical sign is regurgitation. This form is seen in approximately 36-43% of cases. • Generalized MG: Clinical signs include regurgitation secondary to the megaesophagus and exercise induced weakness. This form is seen in approximately 57-64% of cases. • Fulminating MG: Clinical signs include profound weakness to the degree of non-ambulatory tetraparesis/plegia. This form is seen in <5% of cases. 1
A presumptive diagnosis of MG is made based on clinical signs. Previously we had a fun test, the tensilon test, to strongly support the diagnosis. However, edrophonium, the ACh blocker used in this test, is no longer available so this test is no longer performed. To confirm the diagnosis, acetylcholine receptor-antibody (AChR-Ab) tests can be performed in both dogs and cats. Ninety-eight percent of dogs that have acquired MG will demonstrate antibodies, however, 2% will be seronegative. 5 There is no correlation between a higher AChR-Ab level and prognosis in dogs, however, in cats, there is a significant correlation between a higher AChR-Ab titer and a decreased survival time.
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