Novel Management of Masticatory Myositis in Three Dogs with a Selective Janus Kinase (JAK-1) Inhibitor

Abstract

Masticatory myositis (MM) is an inflammatory myopathy reported in dogs and is characterized by inflammation of the masticatory muscles (temporalis, masseter, and pterygoid muscles). Immunosuppressive therapy is the current recommended treatment for MM and may involve glucocorticoids, cyclosporine, azathioprine, mycophenolate mofetil, leflunomide, or a combination of these treatments that are slowly tapered to the lowest effective dose. However, side effects from multimodal medical therapy and complications associated with MM relapses have been reported. The purpose of this case series was to report oclacitinib as a treatment alternative to traditional medical management of MM. The intent of this alternative is to manage side effects from glucocorticoid use. Oclacitinib (1mg/kg per os q12h) was used solely for treatment of MM in three dogs. The dogs were followed up to >6 months after oclacitinib administration. An increase in oral range of motion, as determined by gape angle, was noted in all three dogs. However, a corresponding drop in antibody titers (2M fiber) did not occur. All dogs showed improvement in overall clinical management of MM, side effects from glucocorticoids, and clinical signs related to chronic prednisone use. Larger controlled trials with consistent measurements (interincisal distance, gape angle) and 2M fiber antibody titers are indicated to further assess validation of oclacitinib treatment of MM. The clinical outcome of all dogs was considered successful.

Keywords: 2M antibody; JAK-inhibitor; apoquel; autoimmune; cytokine; masticatory muscle; myopathy; oclacitinib; prednisolone.