Congenital Pseudo-myotonia in Chianina cattle

The authors present a muscle function disorder observed in 11 Chianina animals. The clinical picture is mainly characterized by an exercise-induced muscle contracture which prevents animals from performing muscular activities more intense than a simple walk at a slow pace. In fact, when stimulated to move faster, the muscles immediately become stiff and “freeze up” temporarily, inducing a rigid and uncoordinated gait or bunny hopping. The stiffness disappears as soon as the exercise ceases. If the exercise is prolonged, the stiffness freezes the locomotion and the animals fall on the ground like a log. The animals do not pass out or lose consciousness as in fainting. Retraction of the bulbi and prominence of the third eyelid are other common findings during these startle-elicited crises. Biochemistry usually shows slightly increased levels of creatine kinase, lactate dehydrogenase, aspartate aminotransferase and L-Lactate. Standard needle electromyography showed normal spontaneous insertion activity and voluntary electrical activity. Routine histological preparations as well as more specific histochemical and histoenzymatic stains carried out on bioptic samples of the semimembranosus muscle failed to show any remarkable and helpful findings. Genealogical evaluation of the affected animals revealed common ancestors which might suggest a genetic etiology. On the basis of the clinical findings and of the scanty results obtained by collateral exams, we have adopted the term “Congenital Pseudo-myotonia”. As regards human medicine, the disease in some way resembles the so-called “Brody’s disease”.