Non-inflammatory joint effusions as a presenting sign of hypothyroidism in a dog

Non-inflammatory joint effusion with characteristically increased synovial fluid viscosity is a rare but well-recognised rheumatic manifestation of hypothyroidism in people and based on the literature search, this is the first report of the condition in dogs. A 2-year-old Pyrenean Mountain dog presented for lameness and multiple joint effusions. CT confirmed effusions affecting multiple limb joints along with delayed closure of multiple physes. Synovial fluid analysis from the effused joints showed no evidence of inflammation but the fluid viscosity was markedly increased. Serum total thyroxine concentration was decreased, thyroid-stimulating hormone concentration was increased and antithyroglobulin autoantibody measurement returned a positive result. Oral levothyroxine supplementation resulted in relatively rapid and complete resolution of the clinical signs, in association with attaining a euthyroid state. Follow-up examination and CT six months later confirmed resolution of the joint effusions and significant improvement or resolution of the other documented skeletal changes.