Suspected Congenital Centronuclear Myopathy in an Arabian‐cross Foal

A 6-week-old, Arabian-cross male foal was referred to the Veterinary Teaching Hospital at the Louisiana State University School of Veterinary Medicine for a 1-week history of progressive weakness and intermittent right thoracic limb lameness. The foal had a normal birth, was healthy, had been active, and had not exhibited any abnormalities of gait before presentation. The current owner had acquired the mare just before foaling. The foal presented in sternal recumbency and was unable to rise without assistance. Physical examination identified a quiet, moderately responsive foal with dull mentation and body weight of 64 kg. Rectal temperature was 101.0°F, heart rate was 64 beats/min, and respiratory rate was 28 breaths/min. Mucous membranes were tacky, there was mild decreased skin turgor, and capillary refill time (CRT) was 2 seconds. There was a grade II/VI holosystolic murmur over the left heart base that was considered functional. Increased bronchovesicular sounds were present bilaterally. Lameness (grade 1/5) was evident in the right thoracic limb with pain on palpation and manipulation of the caudal aspect of the distal phalangeal and elbow joints. The lameness resolved after injection of lidocaine (Lidocaine 2%, VetOne ) (2,000 U) into the elbow joint. Joint fluid analysis and radiographs of the distal phalangeal and elbow joints were considered normal. Spinal radiographs, evaluated because of rear limb weakness, also were considered normal. Radiographs of the thorax disclosed ventral alveolar opacities, consistent with aspiration pneumonia. The foal was somnolent on neurological examination and in sternal recumbency, but when assisted it/he could stand and walk. The lower lip drooped bilaterally and the palpebral fissures were decreased bilaterally because of upper eyelid ptosis. Normal palpebral reflexes were present bilaterally and did not fatigue. Normal pupillary light reflexes and dazzle responses were present bilaterally. Spinal reflexes were mildly decreased and muscle mass was decreased symmetrically. Muscle tone was slightly decreased and muscle palpation did not elicit discomfort. Skin sensation, tail function, anal tone, urinary function, and perineal reflex were within normal limits. Posture and conscious proprioception were normal. The gait was short and choppy and the foal could only stand for 15–20 minutes. Generalized muscle weakness and muscle atrophy were diagnosed. Complete blood count results were within reference range. A biochemistry profile showed increased CK (390 U/L; reference range, 0–350 U/L) and AST (439 U/L; reference range, 0–350 U/L) activities, thought to be associated with prolonged recumbency or a myopathy. Tests for WNV and EEE were negative. Botulism was considered less likely because of the absence of dysphagia or abnormal swallowing. Because of the mild dehydration, generalized weakness, pneumonia, and right thoracic limb lameness, the foal was treated with crystalloid fluids (1 L IV then From the Equine Health Studies Program, Department of Veterinary Clinical Sciences, (Polle, Andrews, Gillon, Eades, McConnico); the Department of Comparative Biomedical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA (Strain); the Department of Veterinary Population Medicine, College of Veterinary Medicine, University of Minnesota, Twin Cities, MN (Valberg); and the Comparative Neuromuscular Laboratory, Department of Pathology, University of California, School of Medicine, La Jolla, CA (Guo, Shelton); Dr Polle is presently affiliated with Clinique equine de M eheudin, Ecouch e, France. Corresponding author: F.M. Andrews, Equine Health Studies Program, Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Skip Bertman Drive, Baton Rouge, LA 70803; e-mail: [email protected]. Submitted May 13, 2014; Revised July 22, 2014; Accepted July 23, 2014. Copyright © 2014 by the American College of Veterinary Internal Medicine DOI: 10.1111/jvim.12438 Abbreviations: