G.D. Shelton

Myopathy in horses with pituitary pars intermedia dysfunction (Cushing’s disease)

Fifteen horses with pituitary pars intermedia dysfunction were studied. The horses were of various breeds and between 15 and 28 years of age. Control horses matched for breed and age were studied for comparison. Evaluations included complete blood cell count and serum biochemical analysis, electromyography, and gluteus medius muscle biopsies for histochemical, morphometric, and ultrastructural analysis. No differences were found between groups of horses on routine laboratory analysis or electromyography. We demonstrated that muscle wasting in diseased horses was the result of atrophy of types 2A and 2B muscle fibers and loss of type 2B myofibers. Mild non-specific non-inflammatory myopathic alterations such as myofiber size variation, internal nuclei, perimysial, endomysial and sarcoplasmic fat accumulation were observed. At the ultrastructural level, subsarcolemmal mitochondrial accumulation and increased lipid droplets were evident. Similar to other species, this study confirmed atrophy of type 2 fibers as the cause of muscle mass loss in horses with Cushings disease.

Equine Multiple Acyl‐CoA Dehydrogenase Deficiency (MADD) Associated with Seasonal Pasture Myopathy in the Midwestern United States

BACKGROUND Seasonal pasture myopathy (SPM) is a highly fatal form of nonexertional rhabdomyolysis that occurs in pastured horses in the United States during autumn or spring. In Europe, a similar condition, atypical myopathy (AM), is common. Recently, a defect of lipid metabolism, multiple acyl-CoA dehydrogenase deficiency (MADD), has been identified in horses with AM. OBJECTIVE To determine if SPM in the United States is caused by MADD. ANIMALS Six horses diagnosed with SPM based on history, clinical signs, and serum creatine kinase activity, or postmortem findings. METHODS Retrospective descriptive study. Submissions to the Neuromuscular Diagnostic Laboratory at the University of Minnesota were reviewed between April 2009 and January 2010 to identify cases of SPM. Inclusion criteria were pastured, presenting with acute nonexertional rhabdomyolysis, and serum, urine, or muscle samples available for analysis. Horses were evaluated for MADD by urine organic acids, serum acylcarnitines, muscle carnitine, or histopathology. RESULTS Six horses had clinical signs and, where performed (4/6 horses), postmortem findings consistent with SPM. Affected muscle (4/4) showed degeneration with intramyofiber lipid accumulation, decreased free carnitine concentration, and increased carnitine esters. Serum acylcarnitine profiles (3/3) showed increases in short- and medium-chain acylcarnitines and urinary organic acid profiles (3/3) revealed increased ethylmalonic and methylsuccinic acid levels, and glycine conjugates, consistent with equine MADD. CONCLUSIONS AND CLINICAL IMPORTANCE Similar to AM, the biochemical defect causing SPM is MADD, which causes defective muscular lipid metabolism and excessive myofiber lipid content. Diagnosis can be made by assessing serum acylcarnitine and urine organic acid profiles.

Severe Myositis Associated with Sarcocystis spp. Infection in 2 Dogs

BACKGROUND Dogs are definitive hosts for numerous species of the intracellular protozoan parasite Sarcocystis. Reports of sarcocysts in muscles of dogs most often represent incidental findings. HYPOTHESIS/OBJECTIVES To report the clinicopathologic, ultrastructural, and molecular findings in 2 dogs with myositis associated with Sarcocystis spp. infection, as well as the response to treatment with antiprotozoal drugs. ANIMALS Two dogs with severe myositis in association with massive sarcocystosis. METHODS Retrospective case review. Affected dogs were identified by a diagnostic laboratory. Attending clinicians were contacted, and the medical records reviewed. Immunostaining and electron microscopy were performed on muscle biopsies. Biopsies also were subjected to 18S rRNA gene PCR. RESULTS Both dogs had fever, lymphopenia, thrombocytopenia, and increased serum alanine aminotransferase (ALT) activity when first evaluated. One dog developed hyperbilirubinemia. Subsequently, both dogs had increased serum creatine kinase activity and clinical signs of myositis, with reluctance to move, generalized pain, and muscle wasting. Histopathology of muscle biopsies showed severe inflammatory and necrotizing myopathy with numerous sarcocysts. Ultrastructural studies and 18S rRNA gene sequence results were consistent with infection with a Sarcocystis spp. other than Sarcocystis neurona. Both dogs initially were treated unsuccessfully with clindamycin and anti-inflammatory drugs. One dog died. The other dog subsequently responded to treatment with decoquinate. CONCLUSIONS AND CLINICAL IMPORTANCE Sarcocystis spp. infection should be included in the differential diagnosis for dogs that develop fever, thrombocytopenia, increased liver enzyme activities, and clinical and biochemical evidence of myositis. Although additional studies are required, decoquinate holds promise as an effective treatment for the disease.

Antemortem diagnosis of a distal axonopathy causing severe stringhalt in a horse.

A 16-year-old Westfalian gelding was presented to the Equine Teaching Hospital of Barcelona for a 6week history of a sudden, progressive bilateral abnormal gait in the pelvic limbs. Previous treatment with phenylbutazone and paralumbar corticosteroid (triamcinolone) infiltration had not resulted in improvement. The horse had lived for 2 years in the same pasture with other unaffected horses. None of the other horses developed clinical signs consistent with stringhalt. No history of recent trauma was reported. The horse did not have any previous medical problems, apart from degenerative joint disease of the left radiocarpal and carpometacarpal joints, both metacarpophalangeal joints and both metatarsophalangeal joints that was diagnosed and treated 1 year before presentation. On admission, the horse was excited and reluctant to move, and sedation with xylazine (0.4mg/kg IV) was needed to move the horse out of the van. When eventually moved, the animal showed a bunny-hopping gait with severe and exaggerated flexion movements, and knuckled on both pelvic limbs (supporting information Video S1). Clinical signs were bilateral, but the right pelvic limb seemed more severely affected than the left. The horse kept the right pelvic limb hyperflexed while standing for several minutes until it relaxed. In addition, severe skin abrasions were found on the dorsal aspect of both carpal areas, and on the cannon bone and fetlock areas of both pelvic limbs caused by the abnormal gait. Complete physical and neurological examinations did not identify any other clinically relevant findings. The clinical diagnosis was bilateral stringhalt grade V/V, according to the gradation scale of Huntington et al. Examination of the horse’s pasture revealed very few dry plants, and no evidence of any toxic plant. The horse was fed festuca grass hay similar to other horses in the stable, and the food was in good condition. Results of CBC and serum biochemistry did not disclose any abnormalities. Lumbosacral cerebrospinal fluid collection was attempted, but a sample could not be obtained. Electromyographic (EMG) examination of the pelvic limb muscles including the long digital extensor was attempted with the horse awake to eliminate a peripheral neuropathy or primary myopathy. Unfortunately, the horse was extremely sensitive to any manipulation of the pelvic limbs and conclusive results could not be obtained. To reach a definitive diagnosis, biopsies from the long digital extensor muscle and the superficial peroneal nerve were obtained 4 days after admission. The horse was premedicated with romifidine (0.03mg/kg IV) and butorphanol (0.03mg/kg IV). General anesthesia was induced with diazepam (0.05mg/kg IV) and ketamine (2.2mg/kg IV) and maintained with isofluorane in 100% oxygen with intermittent positive pressure ventilation. The horse was positioned in left lateral recumbency to obtain biopsies from the right pelvic limb. The lateral surface proximal to the tarsus was clipped and surgically prepared. An 8-cm longitudinal incision was made at the level of the lateral and long digital extensor muscle bellies. Superficial tissues were bluntly dissected until the superficial peroneal nerve was identified. The nerve was carefully separated from surrounding connective tissue using sharp dissection and avoiding the use of gauze or blunt dissection to prevent artifact. A 2.5-cm-long fascicular nerve biopsy then was obtained. The sampled nerve then was divided longitudinally into 2 pieces. Dissection was continued cranially until the long digital extensor muscle could be visualized. Two muscle samples were obtained, 1 of standard dimensions (0.5 0.5 1.0 cm) and a smaller sample. The skin was sutured in a discontinuous single pattern using 0USP polypropylene. At the same time, a biopsy from the right middle gluteal muscle was obtained by a percutaneous punch biopsy procedure. One muscle and 1 nerve specimen were placed on a tongue depressor and immersed in 10% formalin. The 2nd specimens were wrapped in saline-moistened gauze sponges and placed into a dry, water-tight container. All samples were shipped overnight under refrigeration to the Comparative Neuromuscular Laboratory, University of California San Diego, La Jolla, California. Immediately upon receipt, unfixed, and chilled muscle and nerve specimens were flash frozen in isopentane precooled in liquid nitrogen, then stored at 801C until further proFrom the Servei de Medicina Interna Equina (Armengou, Monreal); Servei de Neurologia i Neurocirurgia (Añor); Servei de Cirurgia Equina (Climent), Hospital Clı́nic Veterinari, Universitat Autònoma de Barcelona, Barcelona, Spain; and Comparative Neuromuscular Laboratory, Department of Pathology, University of California, San Diego, La Jolla, CA (Shelton). This report was presented at the 2nd Congress of the European College of Equine Internal Medicine (ECEIM), February 2007, Naas, Ireland. The abstract was published in J Vet Intern Med 2007;21:882. Corresponding author: L. Armengou, DVM, Dipl ECEIM, Servei de Medicina Interna Equina, Departament de Medicina i Cirurgia Animals, Facultat de Veterinària, Universitat Autònoma de Barcelona, 08193, Bellaterra, Barcelona, Spain; e-mail: lara.armengou@ uab.cat Submitted July 24, 2009; Revised September 25, 2009; Accepted October 14, 2009. Copyright r 2009 by the American College of Veterinary Internal Medicine 10.1111/j.1939-1676.2009.0437.x Abbreviation:

Sarcoplasmic masses in equine skeletal muscle

Sarcoplasmic masses in humans have been associated with various myopathies, although the significance remains elusive. Similar structures have also been observed in equine muscle. The aim of this study was to determine the frequency of such structures in normal and abnormal equine muscle, and to characterize these structures using histological, histochemical, immunohistochemical, ultrastructural, and morphometric analyses. The histological and histochemical appearance was similar to that of human sarcoplasmic masses with a central or subsarcolemmal distribution. Of interest was a predilection for the gluteus medius muscle in younger horses and type 2B fibers. Ultrastructurally they contained disorganized myofibrils and other cellular components that were not membrane bound and were present in both normal and abnormal equine muscle without a specific disease association, suggesting they are a non-pathological degenerative structure. The relatively frequent occurrence of sarcoplasmic masses in horses may make this species a good model for studying the pathogenesis of these structures.

Risk Factors and Outcomes in Cats with Acquired Myasthenia Gravis (2001–2012)

Background Acquired myasthenia gravis (MG) in cats most commonly causes generalized weakness without megaesophagus and is more often associated with a cranial mediastinal mass, compared to dogs. Hypothesis/Objectives To extend the clinical findings described in the report of 2000 on MG in cats (J Am Vet Med Assoc 215:55–57). Animals Two hundred and thirty‐five cats with MG. Methods Retrospective case study to evaluate the long‐term outcome and incidence of spontaneous remission in myasthenic cats. Information including signalment, clinical presentation, presence of and type of cranial mediastinal mass, treatment including surgical versus medical, survival time, and outcome including spontaneous remissions was collected and analyzed in cats diagnosed at the Comparative Neuromuscular Laboratory, University of California San Diego by detection of acetylcholine receptor antibody titers >0.3 nmol/L by immunoprecipitation radioimmunosassay. Results Acquired MG in cats is associated with a euthanasia rate of 58%. Abyssinian and Somali cats had an increased incidence of MG compared to mixed breed cats or cats of other breeds. A cranial mediastinal mass, most commonly thymoma, was observed in 52% of the cats, which is higher than in the previous report. Spontaneous remission is not a characteristic of MG in cats. Conclusions and clinical importance Myasthenia gravis in cats is a chronic disease associated with a high incidence of a cranial mediastinal mass. Spontaneous remission is not common and clinicians should warn owners of the necessity for long‐term treatment. The clinical outcome with a cranial mediastinal mass did not differ between surgical or medical treatment.

A Novel Movement Disorder in Related Male Labrador Retrievers Characterized by Extreme Generalized Muscular Stiffness

OBJECTIVES To describe the clinical phenotype of a new motor disorder in Labrador Retrievers. ANIMALS AND METHODS Case series study. Seven young male Labrador Retrievers presented for evaluation of stiff gait. RESULTS All affected dogs had generalized muscular stiffness, persistent at rest and resulting in restricted joint movements. They showed a forward flexed posture, festinating gait, and bradykinesia. Signs developed between 2 and 16 months of age and tended to stabilize in adulthood. Needle electromyogram in the conscious state showed continuous motor unit activity in resting epaxial and proximal limb muscles. This activity was abolished by general anesthesia. Muscle and nerve histopathology was normal. In 2 dogs necropsied, astrocytosis was evident throughout the spinal cord gray matter, reticular formation and caudate nuclei. Decreased neuronal counts were selectively found in the spinal cord Rexeds lamina VII, but not in VIII and IX. Pedigree analysis showed that the affected dogs were from 5 related litters. CONCLUSIONS AND CLINICAL IMPORTANCE This new hypertonicity syndrome in Labrador Retrievers is unique because of the selective distribution of the histological lesions, the lack of progression in adulthood, and its exclusive occurrence in male dogs. Pedigree analysis suggests an X-linked hereditary disease, although other modes of inheritance cannot be ruled out with certainty. We hypothesize that altered output from basal nuclei and reticular formation together with motor neuron disinhibition caused by a decreased number of spinal cord interneurons leads to the muscular stiffness.

Recurrent demyelination and remyelination in 37 young Bengal cats with polyneuropathy.

BACKGROUND With the exception of diabetic neuropathy, polyneuropathy associated with hyperchylomicronemia, and a few inherited polyneuropathies, peripheral neuropathies are poorly characterized in cats. A chronic polyneuropathy is described in a cohort of young Bengal cats. OBJECTIVE To characterize the clinical and histopathological features of a chronic-relapsing peripheral neuropathy in young Bengal cats. ANIMALS Thirty-seven young Bengal cats with clinical weakness consistent with peripheral neuropathy. METHODS Bengal cats were included in this study after a diagnosis of polyneuropathy was confirmed by muscle and peripheral nerve biopsy specimens. Pathological changes were characterized at the light and electron microscopic level and by morphometry. Clinical information and long-term outcome from case records of Bengal cats with histologically confirmed peripheral neuropathy were then assessed. RESULTS Nerve fiber loss within distal intramuscular nerve branches was a consistent finding in young Bengal cats with polyneuropathy. The most common abnormalities in peripheral nerve biopsies included inappropriately thin myelin sheaths and thinly myelinated fibers surrounded by supernumerary Schwann cell processes, indicative of repeated cycles of demyelination and remyelination. Recovery was common. Response to treatment could not be determined. CONCLUSIONS AND CLINICAL IMPORTANCE A chronic-relapsing form of polyneuropathy associated primarily with episodes of demyelination and remyelination was identified in young Bengal cats. The prognosis for recovery is good, although relapses are possible and there can be residual motor deficits.

Breed‐Specific Polymyositis in Hungarian Vizsla Dogs

Familial polymyositis in humans has predisposing genetic factors. Descriptions of breed-specific variants of polymyositis in dogs are limited to Newfoundlands and Boxers. A breed-specific myositis in Hungarian Vizslas, marked by pharyngeal dysphagia and masticatory muscle atrophy, occurs in the United Kingdom. In a survey funded by the Vizsla Club of America Welfare Foundation, 16 of 2,505 (0.64%) Vizsla dogs were diagnosed with myositis. Myositis was the 3rd most common disorder affecting nervous tissue or muscles after epilepsy (77 of 2,505; 3.04%) and other cases without a definitive diagnosis (22 of 2,505; 0.88%). In this report we describe 3 unrelated Hungarian Vizslas with masticatory muscle atrophy and pharyngeal dysphagia from across the United States (Pennsylvania, California, Georgia)

Clinical Phenotype of X-Linked Myotubular Myopathy in Labrador Retriever Puppies

Background Seven male Labrador Retriever puppies from 3 different litters, born to clinically normal dams and sires, were evaluated for progressive weakness and muscle atrophy. Muscle biopsies identified a congenital myopathy with pathologic features consistent with myotubular myopathy. Further investigations identified a pathogenic mutation in the myotubularin gene, confirming that these puppies had X‐linked myotubular myopathy (XLMTM). Objective To review the clinical phenotype, electrodiagnostic and laboratory features of XLMTM in this cohort of Labrador Retrievers. Results Male puppies with XLMTM were small and thin compared with their normal littermates. Generalized weakness and muscle atrophy were present by 7 weeks of age in some puppies and evident to most owners by 14 weeks of age. Affected puppies stood with an arched spine and low head carriage, and walked with a short, choppy stride. Muscle atrophy was severe and progressive. Patellar reflexes were absent. Laryngeal and esophageal dysfunction, and weakness of the masticatory muscles occurred in puppies surviving beyond 4 months of age. Serum creatine kinase activity was normal or only mildly increased. EMG findings were nonspecific and included positive sharp waves and fibrillation potentials. Clinical signs progressed rapidly, with most affected puppies unable to walk within 3–4 weeks after clinical signs were first noticed. Conclusions and Clinical Importance Although initial clinical signs of XLMTM are similar to the phenotypically milder centronuclear myopathy in Labrador Retrievers, XLMTM is a rapidly progressive and fatal myopathy. Clinicians should be aware of these 2 distinct myopathies with similar clinical presentations in the Labrador retriever breed.