Clinical features and outcome of acquired myasthenia gravis in 94 dogs

Abstract

Background Factors known to be associated with outcome of acquired myasthenia gravis (MG) in dogs are limited. Hypothesis/Objectives Of dogs with MG, advancing age and comorbid neoplasia are associated with poor long‐term prognosis and low rates of remission. Animals Ninety‐four client‐owned dogs with MG diagnosed by acetylcholine receptor antibody (AChR Ab) assay between 2001 and 2019 from a university clinic and 3 private clinics in the United States. Methods Cases were retrospectively evaluated and data were collected to determine clinical signs, treatment, and response to therapy defined by means of a clinical scoring rubric. Immunological remission was defined as a return of the AChR Ab concentration to <0.6 nmol/L. Multivariable binary logistic regression analysis was used to identify clinical criteria predicting remission. Results An anticholinesterase drug was used to treat 90/94 (96%) dogs, which in 63/94 (67%) was the sole treatment; other drugs included immune modulators. Clinical remission (lack of clinical signs ≥4 weeks after treatment cessation) was observed in 29 (31% [95% confidence interval (CI): 22.4‐40.8%]) dogs, clinical response (lack of clinical signs on treatment) in 14 (15% [95% CI: 9.0‐23.6%]) dogs, clinical improvement (on treatment) in 24 (26% [95% CI: 17.8‐35.2%]) dogs, and no clinical improvement in 27 (29% [95% CI: 20.5‐38.6%]) dogs. Immunological remission was observed in 27/46 (59%) dogs, with clinical remission in all 27. Younger age (P = .04) and comorbid endocrine disease (P = .04) were associated with clinical remission. Initial AChR Ab concentration (P = .02) and regurgitation (P = .04) were negatively associated with clinical remission. Conclusions and Clinical Importance Clinical remission in MG is less likely in older dogs and dogs presenting with regurgitation or high initial AChR Ab concentration, but more likely in younger dogs and dogs with comorbid endocrine disease.

Case report: Immune remission from generalized myasthenia gravis in a dog with a thymoma and cholangiocellular carcinoma

“…The cause for this asymptomatic increase in serum AChR antibody concentration is unknown and the possibility of a spurious result exists given that there are no similar reports in the human literature. Serum AChR concentration has been reported to fluctuate in some dogs with MG without a thymoma before achieving immune remission, however in these cases, the increase or decrease in serum AChR concentration mirrored clinical improvement or deterioration (4,21).…”

“…The resulting clinical presentation is skeletal muscle weakness and fatigability which can affect skeletal muscles focally or in a generalized fashion (1). In 3.4-11% of dogs with MG, the condition is associated with the presence of a cranial mediastinal mass, almost invariably a thymoma, and is thought to represent a paraneoplastic syndrome (3)(4)(5)(6). Several other neoplasms have concurrently been reported in dogs with MG and have been suggested to also cause MG as a paraneoplastic syndrome (7)(8)(9)(10)(11)(12).…”

Seronegative Myasthenia Gravis with Concomitant SARS-CoV-2 Infection in a Dog

“…The neuroanatomical localization was consistent with a generalized lower motor neuron condition. A mild to moderate score (4/5) according to the Muscle Weakness Scoring System [ 9 ] was calculated.…”

Successful Emergency Management of a Dog with Ventilator-Dependent Acquired Myasthenia Gravis with Immunoadsorption

“…Acquired myasthenia gravis (MG) is an autoimmune disease affecting neuromuscular transmission and it is one of the most common neuromuscular disorders in dogs [ 1 , 2 , 3 ]. In this immunologic disease, typically circulating immunoglobulin G autoantibodies, which are directed against a dwindling number of nicotinic acetylcholine receptors (AChR) at the postsynaptic membrane of the neuromuscular junction result in impaired neuromuscular transmission from block alteration or complement-mediated decay of acetylcholine receptors [ 4 , 5 ].…”

“…The treatment goal of acquired myasthenia gravis in dogs is to manage the clinical signs and support survival until spontaneous clinical remission occurs. Aspiration pneumonia and respiratory failure are common causes of death in dogs with acquired MG, and regurgitation was negatively associated with clinical remission in a recent study [ 3 , 6 , 9 , 10 , 11 ]. The common treatment options for myasthenia gravis are the application of acetylcholinesterase inhibitors which increase the half-life of acetylcholine in the synaptic cleft and immunosuppressive therapy, which is primarily offered to dogs that fail to respond to standard treatment and are not suffering from aspiration pneumonia [ 3 , 10 , 12 , 13 ].…”