Multiple myeloma presenting as blepharitis in a horse

Abstract

AbstractMyeloma‐related disorders, including multiple myeloma, extramedullary plasmacytoma, and solid osseous plasmacytoma, are rare in horses. Clinical complaints for myeloma‐related disorders are nonspecific, and when present, M‐protein location is more variable on protein electrophoresis in horses relative to dogs and cats. Here, we describe a case of a 15‐year‐old Thoroughbred mare who presented with recurrent blepharitis. Marked hyperglobulinemia was an incidental finding on routine hematologic and biochemical testing. Bone marrow aspiration consisted of >30% plasma cells, and serum protein electrophoresis demonstrated a monoclonal gammopathy in the alpha 2 fraction leading to a diagnosis of multiple myeloma. Immunofixation and radial immunodiffusion confirmed the presence of an IgG M‐protein. Based on a restricted peak in the alpha 2 location, the specific M‐protein is suspected to be IgG(T), an IgG isotype unique to horses. M‐protein migration in horses is variable relative to dogs and cats, yet immunofixation can still be used to identify equine IgG M‐protein isotypes. The unique clinical presentation in this case also serves as a reminder to consider neoplasia in horses with unusual or nonspecific clinical signs.