CONGENITAL MYOTONIA IN RELATED KITTENS

Four closely related domestic shorthair kittens were investigated foll owing the detection of abnormalities in their gait, difficulty opening their mouths and muscle hypertrophy. They walked with a stiff, stilte d gait, with the stiffness reducing during exercise. Startling of the kittens resulted in hyperextension of the limbs and falling to lateral recumbency, or spasm of the orbicularis oculi muscle, prolonged prola pse of the nictitating membranes and flattening of the ears. One kitte n was intermittently dysphonic. Endotracheal intubation of the anaesth etised kittens was difficult due to an inability to open the mouth to a wide angle, and narrowing of the glottis due to muscle spasm. A diag nosis of congenital myotonia was made based on the clinical signs, the kittens' ages, typical myotonic discharges on electromyography, and t he histopathological and histochemical findings in muscle. This is the first report of congenital myotonia in this species.