Long‐term outcome of cats with acquired myasthenia gravis without evidence of a cranial mediastinal mass

Abstract

Background: Acquired myasthenia gravis (AMG) is increasingly recognized in cats, yet information regarding the natural history of the disease, treatment, and outcome including occurrence of immune and spontaneous remission remains limited.Objective: To determine the long-term outcome of cats with AMG without evidence of a cranial mediastinal mass (CMM).Animals: Eight cats diagnosed with AMG without evidence of a CMM. Methods: Retrospective case series. The medical records of cats diagnosed with AMG between 2005 and 2018 from 2 veterinary referral hospitals were reviewed for inclusion. Inclusion criteria consisted of a diagnosis of AMG, thoracic imaging, serum biochemistry including measurement of creatine kinase, and a CBC. Exclusion criteria were the presence of an identifiable CMM, or administration of methimazole or carbimazole.

Classification of myasthenia gravis and congenital myasthenic syndromes in dogs and cats

“…2,24 Myasthenia gravis can present focally, in a generalized fashion, or in an acute fulminating manner. 19 Myasthenia gravis also can occur with or without a thymoma in dogs and cats, 1,2,4,[18][19][20][21][22][23][24][25][26] or after administration of thiourylene medication in cats, 1,2,[20][21][22][23] and the autoimmune disease mechanism differs based on these factors, 1,2,18,20,22,23 as can treatment, outcome, or both. 1,2,[18][19][20][21][22][23][24][25][26]…”

“…35 As in humans, the autoimmune disease mechanism can affect treatment, outcome, or both, and relates to the presence or absence of a thymoma, or administration of thiourylene medication in cats. 1,2,18,[20][21][22][23][24][25][26] We therefore introduce subgroup classification according to the autoimmune disease mechanism. Lastly, as in humans, NMJ autoantibody testing can be negative in some dogs with generalized MG. 1,27 Such cases must fulfill specific criteria to be referred to as seronegative, including serum AChR autoantibody testing to have been negative at least twice.…”

“…Regardless of the subgroup, certain dogs and cats can present with associated coexisting diseases. 1,31,[36][37][38][39][40][41][42][43] The targeted protein is the AChR, 1,2,[18][19][20][21]24 although striational autoantibodies against titin and the ryanodine receptor are reported in some dogs. 1,44 These striational autoantibodies are typically accompanied by AChR autoantibodies when clinical signs of skeletal muscle weakness and fatigability are present, and are thought not to be pathogenic, hence they are not classified separately, although they might serve as markers of disease severity.…”

“…1,2,4,19,21 This evaluation should be done using thoracic imaging, either thoracic radiography or ideally computed tomography. 24 The incidence of a concurrent cranial mediastinal mass in dogs and cats is F I G U R E 1 Schematic illustration of currently reported CMSs in dogs and cats including the affected neuromuscular compartment, the mechanism of failure of neuromuscular transmission, the affected protein, and the underlying mutated gene. Ac, acetyl; AcCoa, acetyl-coenzyme A; ACh, acetylcholine; AChE, acetylcholinesterase; AChR ε, acetylcholine receptor ε subunit; Ch, choline; ChAT, choline acetyltransferase protein; CHAT, choline acetyltransferase gene; CHRNE, cholinergic receptor nicotinic ε subunit gene; CoA, coenzyme A; COLQ, collagen-like tail subunit of asymmetric acetylcholinesterase gene; CMS, congenital myasthenic syndrome; H + , hydrogen ion 3.4% and 52%, respectively.…”

“…1,2,18,19 However, factors such as the presence or absence of a thymoma, or administration of thiourylene medication in cats, can influence treatment, outcome, or both, frequently leading to the division of affected dogs and cats into separate disease groups based on these factors. 1,2,4,18,[20][21][22][23][24][25][26] Our goal was to review the published literature on MG and CMSs in dogs and cats, and by comparison with published classifications for humans of these 2 conditions, propose a classification system for MG and CMSs in dogs and cats to facilitate their recognition, as well as guide treatment, refine prognosis, and provide a framework for additional studies of these conditions ( Figure 1).…”