Sarcolemmal Specific Collagen VI Deficient Myopathy in a Labrador Retriever

An 11-month-old female spayed Labrador Retriever was presented for examination because of progressive gait abnormality and multiple joint deformities of approximately 6 months’ duration. Mild intermittent lameness of the left thoracic limb was first noticed after exercise when the dog was approximately 5 months of age. Within a month, the lameness had progressed to affect the contralateral thoracic limb. Radiographs of both thoracic limbs revealed a mild mid-diaphyseal varus angulation of the antebrachia. Radiographs of the pelvic limbs revealed moderate right-sided coxofemoral subluxation. At 9 months of age, the dog developed an abnormal pelvic limb posture with bilateral tarsal hyperextension. Resistance to manipulation of multiple limb joints was noted. Synoviocentesis of the right stifle and tarsus was performed and showed slight hyperplasia and hypertrophy of synovial lining cells and negative aerobic and anaerobic culture. Antinuclear antibody and rheumatoid factor titers were negative. Initial treatment with robenacoxib, at a dose of 1 mg/kg PO q24 h resulted in minimal improvement in function. Treatment with tapering doses of prednisolone (10 mg PO q24 h for 5 days, then 5 mg PO q24 h for 5 days, and then 5 mg PO q48 h for 20 days) led to mild gait improvement and range of motion in the affected joints; however, the dog showed progressive difficulty in walking and continuation of the abnormal posture with bilateral carpal and tarsal hyperextension. Serology for Toxoplasma gondii and Neospora caninum was negative. Hydrotherapy and alternating treatment with robenacoxib and prednisolone were continued until referral at the age of 11 months. On examination the dog appeared small in size (body weight 23 kg). The gait was hypometric in all 4 limbs (Video S1). Hyperextension of both carpi, both tarsi, and both stifles was noted (Fig 1). Moderate pelvic and thoracic limb muscle atrophy was apparent and there was moderate bilaterally symmetrical atrophy of the temporalis muscles. Manipulation of the coxofemoral and stifle joints was moderately resisted. Range of motion in the carpi and tarsi was moderately reduced in flexion. Joint laxity was not evident; however, the flat-footed stance suggested possible laxity of the digital flexor tendons (Fig 1, Video S1). Neurologic examination revealed normal thoracic withdrawal and myotatic reflexes. Pelvic limb withdrawal and patellar reflexes were mildly reduced. Hematology and biochemistry revealed a mild increase in potassium at 6.3 mmol/L (reference range 3.5–6.0), alkaline phosphatase (ALP) 131 U/L (reference range 0–50), alanine transaminase (ALT) 124 U/L (reference range 0–25), glutamate dehydrogenase (GLDH) 15 U/L (reference range 0–10), and creatine kinase (CK) 907 U/L (reference range 0–190). The DNA test for hereditary centronuclear myopathy in Labrador retrievers was negative for the PTPLA mutation. Electrodiagnostic testing included electromyography (EMG) of the majority of the muscles on the right side of the body including the temporalis muscle and measurement of the motor nerve conduction velocities of the right sciatic-tibial and left ulnar nerves. EMG revealed spontaneous activity in the gastrocnemius and gluteal muscles. Motor nerve conduction velocities of the left ulnar nerve between the carpus and elbow, and the right From the Southern Counties Veterinary Specialists, Hampshire, UK (Marioni-Henry, Scott, Witte); the New Era Veterinary Hospital, St Saviour, UK (Haworth); and the Department of Pathology, University of California San Diego, La Jolla, CA (Guo, Diane Shelton). Corresponding author: K. Marioni-Henry, Royal (Dick) School of Veterinary Studies, The University of Edinburgh, Hospital for Small Animals, Easter Bush, Veterinary Centre, Roslin, Midlothian EH 25 9RG, UK; e-mail: [email protected]. Submitted May 31, 2013; Revised August 5, 2013; Accepted September 10, 2013. Copyright © 2013 by the American College of Veterinary Internal Medicine 10.1111/jvim.12224 Abbreviations: