Clinical features of idiopathic inflammatory polymyopathy in the Hungarian Vizsla

Successful diagnosis and treatment of canine polymyositis: utilizing MRI and immunohistochemistry for accurate detection

BACKGROUND

Inflammatory myopathy is generally categorized into generalized inflammatory myopathies (gIM), which affect muscles throughout the body, and focal inflammatory myopathies (fIM), which are localized to specific muscles or muscle groups. This report details a case of immune-mediated polymyositis in a dog, successfully diagnosed using MRI and IHC and managed with immunosuppressive therapy.

CASE PRESENTATION

A 5-year-old castrated male Poodle was admitted to our hospital presenting with lethargy and exercise intolerance. Biochemical analysis revealed significantly elevated serum levels of aspartate aminotransferase (AST) and creatine kinase (CK). Physical examination showed muscle atrophy in the hind legs, but further orthopedic and neurological examinations identified no additional abnormalities. MRI demonstrated hyperintense and heterogeneous signal changes across the muscles, including contrast enhancement, suggesting inflammatory myopathy. This diagnosis was confirmed through histopathological examination, which revealed inflammatory lesions with fibrous tissue proliferation within the muscle tissue. To investigate the presence and type of inflammatory cells and vascular changes, aiding in the differential diagnosis of inflammatory myopathies, immunohistochemistry (IHC) was performed, revealing positive findings for CD8+, CD4+, and VEGF in the evaluated tissue, leading to a diagnosis of polymyositis.

CONCLUSIONS

The dog was diagnosed with immune-mediated polymyositis and treatment was initiated with prednisolone at 1 mg/kg twice daily and azathioprine at 2 mg/kg once daily. Following the administration of these immunosuppressive agents, CK levels returned to normal, and the dog's exercise intolerance and lethargy resolved. The thickness of the hind legs also increased progressively. The dog has maintained an improved condition under continued immunosuppressive therapy for four months. This case highlights the critical role of MRI and immunohistochemistry in diagnosing immune-mediated polymyositis, demonstrating their alternative capability in cases where conventional electromyography (EMG) is not feasible in this context.

Novel Management of Masticatory Myositis in Three Dogs with a Selective Janus Kinase (JAK-1) Inhibitor

Masticatory myositis (MM) is an inflammatory myopathy reported in dogs and is characterized by inflammation of the masticatory muscles (temporalis, masseter, and pterygoid muscles). Immunosuppressive therapy is the current recommended treatment for MM and may involve glucocorticoids, cyclosporine, azathioprine, mycophenolate mofetil, leflunomide, or a combination of these treatments that are slowly tapered to the lowest effective dose. However, side effects from multimodal medical therapy and complications associated with MM relapses have been reported. The purpose of this case series was to report oclacitinib as a treatment alternative to traditional medical management of MM. The intent of this alternative is to manage side effects from glucocorticoid use. Oclacitinib (1mg/kg per os q12h) was used solely for treatment of MM in three dogs. The dogs were followed up to >6 months after oclacitinib administration. An increase in oral range of motion, as determined by gape angle, was noted in all three dogs. However, a corresponding drop in antibody titers (2M fiber) did not occur. All dogs showed improvement in overall clinical management of MM, side effects from glucocorticoids, and clinical signs related to chronic prednisone use. Larger controlled trials with consistent measurements (interincisal distance, gape angle) and 2M fiber antibody titers are indicated to further assess validation of oclacitinib treatment of MM. The clinical outcome of all dogs was considered successful.

Pathologic Changes in and Immunophenotyping of Polymyositis in the Dutch Kooiker Dog

Earlier, we described a breed-specific inflammatory myopathy in Dutch Kooiker dogs (Het Nederlandse Kooikerhondje), one of the nine Dutch breeds. The disease commonly manifests itself with clinical signs of difficulty walking, muscle weakness, exercise intolerance, and/or dysphagia. In nearly all dogs' creatine kinase (CK) activity was elevated. Histopathology reveals the infiltration of inflammatory cells within the skeletal muscles. The objective of this study was to further investigate and characterize the histopathological changes in muscle tissue and immunophenotype the inflammatory infiltrates. FFPE fixed-muscle biopsies from 39 purebred Kooiker dogs were included and evaluated histopathologically according to a tailored classification scheme for skeletal muscle inflammation. As in other breed-related inflammatory myopathies, multifocal, mixed, and predominantly mononuclear cell infiltration was present, with an initial invasion of viable muscle fibres and the surrounding stroma leading to inflammation, necrosis, and tissue damage. Immunophenotyping primarily revealed lymphohistiocytic infiltrates, with CD3+ T-cells being the predominant inflammatory cell type, accompanied by CD8+ cytotoxic T-cells. The concurrent expression of MHC-II class molecules on myofibres suggests their involvement in initiating and maintaining inflammation. Additionally, CD20+ B-cells were identified, though in lower numbers compared to T-cells, and IBA-1-positive macrophages were frequently seen. These findings suggest a breed-specific subtype of polymyositis in Kooiker dogs, akin to other breeds. This study sheds light on the immune response activation, combining adaptive and innate mechanisms, contributing to our understanding of polymyositis in this breed.

An Inflammatory Myopathy in the Dutch Kooiker Dog

The Dutch Kooiker dog (het Nederlandse Kooikerhondje) is one of nine Dutch dog breeds. As of 1960, a number of heritable diseases have been noted in this breed. One is an inflammatory myopathy that emerged in 1972, with numbers of affected dogs gradually increasing during the last few decades. The objective of this paper is to describe clinical signs, laboratory results, electromyography and histopathology of the muscle biopsies of the affected dogs. Method: Both retrospectively as well as prospectively affected Kooiker dogs were identified and categorized using a Tiered level of Confidence. Results: In total, 160 Kooiker dogs-40 Tier I, 33 Tier II and 87 Tier III-were included. Clinical signs were (1) locomotory problems, such as inability to walk long distances, difficulty getting up, stiff gait, walking on eggshells; (2) dysphagia signs such as drooling, difficulty eating and/or drinking; or (3) combinations of locomotory and dysphagia signs. CK activities were elevated in all except for one dog. Histopathology revealed a predominant lymphohistiocytic myositis with a usually low and variable number of eosinophils, neutrophils and plasma cells. It is concluded that, within this breed, a most likely heritable inflammatory myopathy occurs. Further studies are needed to classify this inflammatory myopathy, discuss its treatment, and unravel the genetic cause of this disease to eradicate it from this population.

Clinical characteristics of non-infectious inflammatory myopathy in the boxer dog

OBJECTIVES

To evaluate the clinical characteristics, treatment, outcome and potential association between non-infectious inflammatory myopathy and malignancy in boxer dogs.

MATERIALS AND METHODS

Boxer dogs histologically diagnosed with non-infectious inflammatory myopathy at the Comparative Neuromuscular Laboratory, University of California San Diego from 2010 to 2018 and with complete medical records were included in this retrospective study. Signalment, history, clinical signs, clinicopathologic findings, treatment and outcome were documented.

RESULTS

Twenty-eight boxer dogs with non-infectious inflammatory myopathy, aged 1 to 11 years, were included. Eighteen were male (16 neutered; two entire) and 10 were female (seven spayed; three entire). Clinical signs included generalised weakness (n=17), dysphagia (n=11) and weight loss (n=10). Serum creatine kinase activity was elevated in all 20 cases tested (range 908 to 138,000 IU/L). One dog had undifferentiated round cell neoplastic infiltration within the muscle at the time of inflammatory myopathy diagnosis. Five dogs historically had mast cell tumours and 21 dogs were not diagnosed with neoplasia prior, at the time of or after inflammatory myopathy diagnosis. Treatment included glucocorticoid monotherapy (n=12), cyclosporine monotherapy (n=1) or multiple immune-suppressive medications (n=14). Six dogs neurologically improved, 11 improved but relapsed while on treatment, seven did not improve. Eight dogs were euthanased, one died, four were lost to follow-up.

CLINICAL SIGNIFICANCE

Boxer dogs with non-infectious inflammatory myopathy can present for generalised weakness and dysphagia; long-term successful outcome is uncommon. The relationship between neoplasia and non-infectious inflammatory myopathy in boxer dogs remains unclear; future prospective studies evaluating a larger cohort are warranted.

Surgical stabilisation of hiatal hernia and gastroesophageal reflux associated with idiopathic inflammatory polymyopathy in a Wire Fox Terrier

A one-and-a-half-year-old male Wire Fox Terrier weighing 3 kg presented with continuous drooling and vomiting. Its body condition score was 3/9, and severe atrophy of the temporal/masticatory muscle, trismus, and enophthalmos was observed on physical examination. The radiographic examination and fluoroscopic oesophagography revealed a type 1 hiatal hernia with gastroesophageal reflux. The serology tests revealed increased muscle enzyme activities. The antibody tests for acetylcholine receptor, type 2M fibre, and infectious agents were negative. A conventional surgical treatment was performed, and a thickened, stretched, and flaccid diaphragmatic muscle and an extended inelastic oesophageal hiatus were observed. On the histological examination of the diaphragmatic muscle, a diffuse histiocytic myositis was confirmed. Although the postoperative gastroesophageal reflux totally disappeared, the oesophageal motility and clinical signs did not improve significantly. Medical treatment with immunosuppressive agents was attempted and was effective in alleviating the clinical signs and abnormal oesophageal motility. The health condition of the dog was adequately maintained in the 12-month monitoring period. These findings suggest that, although the medical and surgical treatment have different therapeutic effects, they should be considered simultaneously for the management of a hiatal hernia associated with polymyopathy in dogs.

Treatment Outcome of 22 Dogs With Masticatory Muscle Myositis (1999-2015)

Medical records of dogs diagnosed with masticatory muscle myositis (MMM) at Ryan Veterinary Hospital of the University of Pennsylvania during a period of 17 years (from 1999 to 2015) were reviewed. Twenty-two dogs were included in this retrospective case series study. Immunosuppressive doses of prednisone were prescribed to all dogs. Twenty dogs had full recovery of masticatory function. The mean (SD) improvement in the vertical mandibular range of motion (vmROM) was 5.3 (3.1) cm during the first 4 weeks of treatment (weeks 1-4) and 2.8 (2.2) cm during the subsequent 8 weeks (weeks 5-12). The vmROM continued to improve for several more months. Six dogs had a relapse, but the clinical signs were more severe in dogs when no longer receiving prednisone compared to dogs still on prednisone at the time of relapse. When diagnosed and treated appropriately, MMM has a good prognosis with relatively quick return to masticatory function. Early discontinuation of prednisone therapy should be avoided. Approximately 1 year of therapy is recommended prior to discontinuing the medication. Educating the client about how to perform muscle palpation, determine vmROM at home, recognize signs of pain, and notice behavioral changes may help in the early detection of relapses.

Magnetic resonance imaging of masticatory muscles in basset hounds

OBJECTIVES

To describe low- and high-field MRI characteristics of occult masticatory muscle lesions in basset hounds.

MATERIALS AND METHODS

Retrospective review of the MR images of the heads of 44 basset hounds that had been imaged for reasons unrelated to suspected muscle disease.

RESULTS

In most basset hounds, there was reduced bulk of the superficial part of the temporalis and masseter muscles together with bilaterally symmetrical T2W and T1W hyperintense signal with reduced contrast enhancement compared to normal muscle. Interpretation of various pulse sequences suggested that the affected muscle areas contained adipose tissue with no evidence of inflammation, and this was confirmed on biopsy in one dog. This pattern of changes is different from MRI changes in inflammatory myopathies.

CLINICAL SIGNIFICANCE

Poor muscle bulk and MRI signal changes in the superficial parts of the temporalis and masseter muscles in basset hounds appear to be normal findings in this breed and should not be misinterpreted as evidence of an inflammatory myopathy.