Canine inflammatory myopathy: Analysis of cellular infiltrates

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.

Polyautoimmunity manifest as inflammatory myopathy, uveitis, and progressive cutaneous depigmentation in a mixed breed dog: a case report

BACKGROUND

Polyautoimmunity is the expression of more than one autoimmune disease in a single patient. This report documents polyautoimmunity in a mixed breed dog with concurrent uveitis, cutaneous depigmentation, and inflammatory myopathy.

CASE PRESENTATION

A 1-year-old male neutered mixed breed dog was presented for progressive generalized leukotrichia and leukoderma, bilateral panuveitis, and masticatory muscle atrophy. The latter progressed to myositis of lingual, pharyngeal, and masticatory muscles confirmed by biopsy. Temporalis muscle was completely replaced by adipose and fibrous tissue, and necrotic myofibers with extensive infiltration of mononuclear cells indicated active myositis of lingual muscle. Skin biopsies showed severe melanin clumping in epidermis, hair follicles, and hair shafts, and perifollicular pigmentary incontinence. Uveitis, depigmentation, and myositis affecting the masticatory, pharyngeal, and tongue muscles were diagnosed based on clinical, histological, and laboratory findings.

CONCLUSIONS

To the authors' knowledge, this is the first report of concurrent uveitis, progressive cutaneous depigmentation, and inflammatory myopathy in a dog.

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 presentation, MRI, histopathology and outcome in a cat with immune-mediated masticatory myositis

CASE SUMMARY

A 4-year-old female spayed domestic shorthair cat was presented with facial swelling, ocular discharge and intermittent bilateral exophthalmos. Haematology revealed mild eosinophilia. Serum biochemistry showed a markedly elevated creatine kinase activity. MRI of the head revealed diffuse and severe changes of the masticatory muscles, including irregular areas compatible with fluid or necrosis within the abnormal muscle tissue. Cytological analysis of the left temporal muscle revealed eosinophilic and macrophagic inflammation. Bacterial and fungal cultures were negative. Serological titres against Toxoplasma gondii were compatible with previous exposure. A canine ELISA against masticatory muscle type IIM fibre proteins was positive at 1:4000 (reference interval <1:100). Histopathological examination of the left temporalis muscle revealed moderately severe and multifocal myositis. A diagnosis of immune-mediated masticatory myositis was made and immunosuppressive therapy was started. The cat initially responded to tapering doses of prednisolone, but subsequent relapses required therapy modulation. At the time of writing, 27 months after the initial diagnosis, the cat was in remission, but was diagnosed with diabetes mellitus, probably secondary to chronic glucocorticoid use.

RELEVANCE AND NOVEL INFORMATION

To our knowledge, this is the first case report to describe the MRI appearance of masticatory myositis in a cat and the second to describe the clinical presentation, histopathology, response to treatment and outcome in a cat with this condition.

Myositis, Ganglioneuritis, and Myocarditis with Distinct Perifascicular Muscle Atrophy in a 2-Year-Old Male Boxer

A 2-year-old male, intact Boxer was referred for chronic diarrhea, hyporexia, labored breathing, weakness and elevated creatine kinase, and alanine aminotransferase activities. Initial examination and diagnostics revealed a peripheral nervous system neurolocalization, atrial premature complexes, and generalized megaesophagus. Progressive worsening of the dog's condition was noted after 36 h; the dog developed aspiration pneumonia, was febrile and oxygen dependent. The owners elected humane euthanasia. Immediately postmortem biopsies of the left cranial tibial and triceps muscles and the left peroneal nerve were obtained. Postmortem histology revealed concurrent myositis, myocarditis, endocarditis, and ganglioneuritis. Mixed mononuclear cell infiltrations and a distinct perifascicular pattern of muscle fiber atrophy was present in both muscles. This is a novel case of diffuse inflammatory myopathy with a distinct perifascicular pattern of atrophy in addition to endocarditis, myocarditis, and epicarditis.

Inflammatory Myopathy in Horses With Chronic Piroplasmosis

Horses affected by chronic piroplasmosis may develop poor performance and muscle atrophy. Here we investigate the pathological and immunopathological aspects of myopathy occurring in chronic equine piroplasmosis. The study included 16 horses serologically positive for equine piroplasms presenting with clinical signs and supporting serum biochemical evidence of a myopathy. Skeletal muscle was evaluated by histopathology, immunohistochemistry, indirect immunofluorescence, and molecular detection of piroplasms and inflammatory cytokines in skeletal muscle. Histologic lesions included muscle fiber atrophy (100% of cases), degenerative changes (13/16, 81%), and perivascular perimysial and endomysial lymphocytic infiltrates (81% of cases). In 15 cases (94%), muscle fibers had strong immunostaining for major histocompatibility complex classes I and II. T lymphocyte populations were mainly CD3+, CD8+, and CD4+ in equal proportions, with a lower number of CD79α+ cells. The serum from affected horses was tested by indirect immunofluorescence for binding of IgG, IgM, or IgA to sections of normal equine muscle to detect circulating autoantibodies against muscle antigen(s). In all cases, distinct sarcolemmal staining was detected in sections incubated with serum from affected horses, in contrast to sections incubated with phosphate-buffered saline or equine control sera. Reverse transcription polymerase chain reaction (RT-PCR) testing of muscles from affected animals revealed a significant increase of interferon-γ, interleukin-12, and tumor necrosis factor-α gene expression compared to healthy controls. Theileria equi or Babesia caballi was not detected in samples of affected muscle by RT-PCR. Thus, inflammatory myopathy associated with equine piroplasmosis may involve an autoimmune pathogenesis with upregulation of inflammatory cytokines that may cause myofiber atrophy and degeneration.

MASTICATORY MUSCLE MYOSITIS IN A GRAY WOLF (CANIS LUPUS)

A 10-yr-old male, neutered gray wolf ( Canis lupus ) was presented for atrophy of the temporalis and masseter muscles. Clinical signs and magnetic resonance imaging were consistent with a myopathy. Positive serology for antibody titers directed against Type 2M myofibers, and the observation of a mixed mononuclear inflammatory cell infiltrate along with eosinophils and neutrophils within the temporalis muscle, were diagnostic for masticatory muscle myositis. Importantly, protozoal myositis was excluded based on other clinicopathologic data. The case highlights the potential for immune-mediated polymyositis in canids other than the domesticated dog ( Canis lupus familaris). Additionally, awareness of a diet in which raw meat is used should prompt a thorough investigation for an underlying infectious myositis in the gray wolf.

Immune-Mediated Muscle Diseases of the Horse

In horses, immune-mediated muscle disorders can arise from an overzealous immune response to concurrent infections or potentially from an inherent immune response to host muscle antigens. Streptococcus equi ss. equi infection or vaccination can result in infarctive purpura hemorrhagica (IPH) in which vascular deposition of IgA-streptococcal M protein complexes produces ischemia and complete focal infarction of skeletal muscle and internal organs. In Quarter Horse–related breeds with immune-mediated myositis, an apparent abnormal immune response to muscle antigens results in upregulation of major histocompatibility complex class (MHC) I and II on muscle cell membranes, lymphocytic infiltration of lumbar and gluteal myofibers, and subsequent gross muscle atrophy. Rarely, an inflammatory event results in myositis with subsequent systemic calcinosis characterized by a pathognomonic hyperphosphatemia and high fatality rate. This review presents an overview of these immune-mediated myopathies and highlights clinical and pathological features as well as the suspected pathophysiology.

Clinical Implications and Hospital Outcome of Immune-Mediated Myositis in Horses

BACKGROUND

Immune-mediated myositis (IMM) is a cause of rhabdomyolysis, stiffness, and muscle atrophy predominantly affecting Quarter horses. Limited information is available with regard to outcome, prognostic indicators, and associations with concurrent diseases.

HYPOTHESIS/OBJECTIVES

To report outcomes and associations between outcome and clinical and laboratory parameters, and presence of concurrent illness.

ANIMALS

Sixty-eight horses; 52 Quarter horses and related breeds and 16 other breeds.

METHODS

Retrospective cohort study (1991-2014). Medical records of horses with histological diagnosis of IMM were reviewed. Data recovery included signalment, laboratory variables, therapy, and outcome. Logistic regression was used to quantify the association between potential prognostic factors and survival to discharge.

RESULTS

Quarter horses were younger (mean < 4 years, range 3 months-21 years) than other breeds (mean < 10 years, range 1-23 years). Pathogens causing concurrent or recent infection included S. equi equi, S. equi zooepidemicus, C. pseudotuberculosis, Anaplasma phagocytophilum, herpes virus-1, and influenza. The most common clinical signs consisted of rapidly progressive diffuse symmetrical muscle atrophy (80%), stiff gait (74%), and fever (44%). All horses that received medical therapy immediately upon admission survived to discharge (survival proportion = 87%). Leucocytosis was a common finding (60%). Horses with concurrent fever and other illness had a poor prognosis for hospital discharge.

CONCLUSIONS AND CLINICAL IMPORTANCE

Horses with IMM can have a favorable outcome. Horses with concurrent fever and another illness had decreased probability of survival to discharge.

Major Histocompatibility Complex I and II Expression and Lymphocytic Subtypes in Muscle of Horses with Immune-Mediated Myositis

BACKGROUND

Major histocompatibility complex (MHC) I and II expression is not normally detected on sarcolemma, but is detected with lymphocytic infiltrates in immune-mediated myositis (IMM) of humans and dogs and in dysferlin-deficient muscular dystrophy.

HYPOTHESIS/OBJECTIVES

To determine if sarcolemmal MHC is expressed in active IMM in horses, if MHC expression is associated with lymphocytic subtype, and if dysferlin is expressed in IMM.

ANIMALS

Twenty-one IMM horses of Quarter Horse-related breeds, 3 healthy and 6 disease controls (3 pasture myopathy, 3 amylase-resistant polysaccharide storage myopathy [PSSM]).

METHODS

Immunohistochemical staining for MHC I, II, and CD4+, CD8+, CD20+ lymphocytes was performed on archived muscle of IMM and control horses. Scores were given for MHC I, II, and lymphocytic subtypes. Immunofluorescent staining for dysferlin, dystrophin, and a-sarcoglycan was performed.

RESULTS

Sarcolemmal MHC I and II expression was detected in 17/21 and 15/21 of IMM horses, respectively, and in specific fibers of PSSM horses, but not healthy or pasture myopathy controls. The CD4+, CD8+, and CD20+ cells were present in 20/21 IMM muscles with CD4+ predominance in 10/21 and CD8+ predominance in 6/21 of IMM horses. Dysferlin, dystrophin, and a-sarcoglycan staining were similar in IMM and control muscles.

CONCLUSIONS AND CLINICAL IMPORTANCE

Deficiencies of dysferlin, dystrophin, and a-sarcoglycan are not associated with IMM. Sarcolemmal MHC I and II expression in a proportion of myofibers of IMM horses in conjunction with lymphocytic infiltration supports an immune-mediated etiology for IMM. The MHC expression also occured in specific myofibers in PSSM horses in the absence of lymphocytic infiltrates.

Clinical features of idiopathic inflammatory polymyopathy in the Hungarian Vizsla

BACKGROUND

A retrospective study of the clinicopathological features of presumed and confirmed cases of idiopathic inflammatory polymyopathy in the Hungarian Vizsla dog and guidelines for breeding.

RESULTS

369 medical records were reviewed (1992-2013) and 77 Hungarian Vizslas were identified with a case history consistent with idiopathic inflammatory polymyopathy. Inclusion criteria were: group 1 (confirmed diagnosis); histopathology and clinical findings compatible with an inflammatory polymyopathy and group 2 (probable diagnosis); clinical findings compatible with a polymyopathy including dysphagia, sialorrhea, temporal muscle atrophy, elevated serum creatine kinase (CK) activity, and sufficient clinical history to suggest that other neuromuscular disorders could be ruled out. Some group 2 dogs had muscle biopsy, which suggested muscle disease but did not reveal an inflammatory process. The mean age of onset was 2.4 years; male dogs were slightly overrepresented. Common presenting signs were dysphagia, sialorrhea, masticatory muscle atrophy, and regurgitation. Common muscle histopathological findings included degenerative and regenerative changes, with multifocal mononuclear cell infiltration with lymphoplasmacytic myositis of variable severity. A positive response to immunosuppressive treatment supported an immune-mediated aetiology. The mean age at death and survival time were 6.4 and 3.9 years, respectively. Recurrence of clinical signs and aspiration pneumonia were common reasons for euthanasia.

CONCLUSIONS

Diagnosis of Vizsla idiopathic inflammatory polymyopathy can be challenging due to lack of specific tests, however the presence of dysphagia, regurgitation and masticatory muscle atrophy in this breed with negative serological tests for masticatory muscle myositis and myasthenia gravis, along with muscle biopsies suggesting an inflammatory process, support the diagnosis. However, there is an urgent need for a more specific diagnostic test. The average of inbreeding coefficient (CoI) of 16.3% suggests an increased expression of a Dog Leukocyte Antigen Class II haplotype, leading to an increased disease risk. The prognosis remains guarded, as treatment can only manage the disease. Recurrence of clinical signs and perceived poor quality of life are the most common reasons for humane euthanasia.

Necrotizing and eosinophilic masticatory myositis in farmed mink: a preliminary description

This report describes necrotizing and eosinophilic myositis affecting the masticatory muscles of a group of mink. Affected animals demonstrated sudden death with marked subcutaneous oedema over the dorsal head. The temporalis and masseter muscles were pale, swollen and friable. Histologic changes consisted of varying degrees of myodegeneration, myonecrosis and inflammation. Eosinophils were prominent in the inflammatory infiltrate. Similar to dogs, masticatory muscles in mink were found to contain unique type 2M fibres, suggesting a possible target for an immune response. Aerobic and anaerobic tissue cultures of the affected musculature revealed no significant pathogens. Histological and nutritional analyses were not typical of vitamin E/selenium deficiency. This case series supports the existence of a novel disease entity in mink with some features comparable with masticatory muscle myositis in dogs.

Use of MRI for the Early Diagnosis of Masticatory Muscle Myositis

The medical records of two dogs that were diagnosed with masticatory muscle myositis (MMM) were reviewed. The reported clinical signs included intense pain when opening the mouth and restricted jaw movement. MRI detected widespread, symmetrical, and inhomogeneously hyperintense areas in the masticatory muscle. Electromyography (EMG) demonstrated severe and spontaneous pathologic activity in the temporal and masseter muscles. With early therapeutic treatment, remission of symptoms occurred within 2 mo, and no relapses were observed for the subsequent 2 yr. The gold standard for the diagnosis of MMM is the 2M antibody test, but the purpose of this study was to evaluate the use of MRI as an accurate and efficient diagnostic tool for the initiation of early therapy for the treatment of muscle myositis.

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.

Polymyositis following Vogt-Koyanagi-Harada-like syndrome in a Jack Russell terrier

A male Jack Russell terrier developed bilateral uveitis and glaucoma at 1 year of age. Since the ocular disease was painful and unresponsive to treatment, both globes were enucleated. Microscopical evaluation of one enucleated globe revealed panuveitis, with pigment dispersion and phagocytosis consistent with the ocular lesions of canine Vogt-Koyanagi-Harada (VKH)-like syndrome. Three years later the dog was represented with severe muscle disease and skin lesions. Due to rapid clinical deterioration the dog was humanely destroyed. Necropsy examination revealed lichenoid interface inflammation in the skin and mucous membranes, with pigmentary incontinence consistent with VKH-like syndrome and lymphocytic and histiocytic polymyositis with marked muscle atrophy. Canine VKH-like syndrome is an autoimmune disease that targets melanocyte antigens. Some human patients with VKH disease develop additional autoimmune diseases. To our knowledge this is the first reported case of polymyositis subsequent to VKH-like disease in a dog. In addition, VKH-like disease has not been previously reported in a Jack Russell terrier.

Inflammatory Myopathy with Severe Tongue Atrophy in Pembroke Welsh Corgi Dogs

A disease characterized by tongue and facial muscle atrophy has been recognized sporadically among Pembroke Welsh Corgi (PWC) dogs in Japan. The present study describes the pathologic findings of this canine syndrome. Histopathologic examinations were performed in 2 dogs, including a case of muscular biopsy. Identification and characterization of autoantibodies were attempted by fluorescent antibody test (FAT) and Western blot (WB) by using sera from 7 PWC dogs with typical clinical features, 6 PWC dogs with other clinical signs, and 2 from other breeds with polymyositis. Clinically, the 7 affected PWC dogs exhibited dysphagia with severe tongue atrophy, facial muscular atrophy, and occasional walking difficulty. Histopathologic examinations of the 2 dogs with clinical symptoms revealed moderate to severe inflammatory lesions characterized by lymphohistiocytic infiltration and muscular atrophy in the tongue and/or femoral muscles. The tongue lesions were very severe and accompanied by diffuse fatty infiltration. There were no major lesions in the nervous tissues examined. By FAT, an autoantibody against the cross striation of skeletal muscle was detected in sera from 5 affected PWC dogs. By using WB analysis, the autoantibodies recognized a 42-kDa molecule in striated muscle but not in the nervous tissues. All of the findings indicated that the unique disease of PWC dogs might be generalized inflammatory myopathy, whereas the detailed etiology concerning the dominant involvement of tongue muscles and the role of the autoantibody in the canine disease remain to be clarified.

Life threatening complication associated with anesthesia in a dog with masticatory muscle myositis

OBJECTIVE

To report a serious complication in a dog with masticatory muscle myositis (MMM) that occurred during general anesthesia for diagnostic testing.

STUDY DESIGN

Case report.

ANIMALS

A 2-year-old male Pug.

METHODS

MMM was diagnosed in a Pug with a 2-week history of trismus by electrodiagnostics, histopathology, and 2M antibody test. During anesthesia tongue protrusion occurred and because of trismus, an inability to reposition the tongue resulted in venous congestion and severe swelling. Forceful physical attempts and subsequent removal of the rostral digastricus and masseter muscle attachments from the mandible did not increase jaw mobility. Mandibular symphysiotomy was necessary to resolve lingual venous congestion and to reposition the tongue into the oral cavity.

RESULTS

Tongue swelling rapidly subsided after symphysiotomy allowing the tongue to be repositioned into the oral cavity. After treatment of MMM with corticosteroids, jaw range of motion improved and at 6 months was approximately 70% normal.

CONCLUSIONS

Trismus could not be overcome by detachment of the masseter and digastricus muscle insertions from the mandible, and symphysiotomy was required to reposition the tongue in the oral cavity.

CLINICAL RELEVANCE

In dogs with MMM, tongue position should be monitored during anesthesia to avoid inadvertent protrusion and swelling from venous congestion. Use of anesthetic monitoring equipment on the tongue, such as a pulse oximeter probe, should be avoided in these patients.

Vacuolar myopathy in a dog resembling human sporadic inclusion body myositis

Sporadic inclusion body myositis (sIBM) is the most common myopathy in people over the age of 50 years. While immune-mediated inflammatory myopathies are well documented in dogs, sIBM has not been described. An 11-year-old dog with chronic and progressive neuromuscular dysfunction was evaluated for evidence of sIBM using current pathologic, immunohistochemical and electron microscopic diagnostic criteria. Vacuoles and congophilic intracellular inclusions were identified in cryostat sections of multiple muscle biopsies and immunostained with antibodies against amyloid-β peptide, amyloid-β precursor protein, and proteosome 20S of the ubiquitin–proteosome system. Cellular infiltration and increased expression of MHC Class I antigen were observed. Cytoplasmic filamentous inclusions, membranous structures, and myeloid bodies were identified ultrastructurally. These observations constitute the first evidence that both the inflammatory and degenerative features of human sIBM can occur in a non-human species.

Necrotizing Meningoencephalitis in Five Chihuahua Dogs

An acute to chronic idiopathic necrotizing meningoencephalitis was diagnosed in 5 Chihuahua dogs aged between 1.5 and 10 years. Presenting neurologic signs included seizures, blindness, mentation changes, and postural deficits occurring from 5 days to 5.5 months prior to presentation. Cerebrospinal fluid analyses from 2 of 3 dogs sampled were consistent with an inflammatory disease. Magnetic resonance imaging of the brain of 2 dogs demonstrated multifocal loss or collapse of cortical gray/white matter demarcation hypointense on T1-weighted images, with T2-weighted hyperintensity and slight postcontrast enhancement. Multifocal asymmetrical areas of necrosis or collapse in both gray and white matter of the cerebral hemispheres was seen grossly in 4 brains. Microscopically in all dogs, there was a severe, asymmetrical, intensely cellular, nonsuppurative meningoencephalitis usually with cystic necrosis in subcortical white matter. There were no lesions in the mesencephalon or metencephalon except in 1 dog. Immunophenotyping defined populations of CD3, CD11d, CD18, CD20, CD45, CD45 RA, and CD79a immunoreactive inflammatory cells varying in density and location but common to acute and chronic lesions. In fresh frozen lesions, both CD1b,c and CD11c immunoreactive dendritic antigen-presenting cells were also identified. Immunoreactivity for canine distemper viral (CDV) antigen was negative in all dogs. The clinical signs, distribution pattern, and histologic type of lesions bear close similarities to necrotizing meningoencephalitis as described in series of both Pug and Maltese breed dogs and less commonly in other breeds.

Autoantibodies in Canine Masticatory Muscle Myositis Recognize a Novel Myosin Binding Protein-C Family Member

Inflammatory myopathies are a group of autoimmune diseases that affect muscles. In humans, the most common inflammatory myopathies are polymyositis, dermatomyositis, and inclusion body myositis. Autoantibodies may be found in humans with inflammatory myopathies, and these play an important role in diagnosis and disease classification. However, these Abs are typically not muscle specific. Spontaneously occurring canine inflammatory myopathies may be good parallel disorders and provide insights into human myositis. In dogs with inflammatory myopathy, muscle-specific autoantibodies have been found, especially in masticatory muscle myositis. We have identified the major Ag recognized by the autoantibodies in canine masticatory muscle myositis. This Ag is a novel member of the myosin binding protein-C family, which we call masticatory myosin binding protein-C (mMyBP-C). mMyBP-C is localized not only within the masticatory muscle fibers, but also at or near their cell surface, perhaps making it accessible as an immunogen. The gene for mMyBP-C also exists in humans, and mMyBP-C could potentially play a role in certain human inflammatory myopathies. Understanding the role of mMyBP-C in this canine inflammatory myopathy may advance our knowledge of mechanisms of autoimmune inflammatory muscle diseases, not only in dogs, but also in humans.

Magnetic resonance imaging and pathological findings in a case of canine idiopathic eosinophilic meningoencephalitis

A case of idiopathic eosinophilic meningoencephalitis in a six-month-old male Maremma shepherd dog is reported. The dog was referred with a four month history of progressive weakness and depression with loss of trained habits. Tendency to recumbency, disorientation, visual impairment, bilaterally decreased menace response and hindlimb conscious proprioception deficits were detected. Magnetic resonance imaging showed a diffuse hypointense signal involving the cerebral grey matter with enlargement of the cerebral sulci on T1-weighted and fast fluid-attenuated inversion recovery (FLAIR) sequences consistent with a diffuse necrosis or atrophy of the cortical grey matter. Histological examination revealed severe inflammatory infiltration mainly composed of eosinophils and macrophages in the subarachnoid space and in the superficial layer of the cerebral cortex where parenchymal rarefaction and necrosis of neurones were also evident. No parasites, cysts or fungi were detected, and an immunologically mediated disorder was suspected. Magnetic resonance imaging may represent a useful diagnostic tool to differentiate idiopathic eosinophilic meningoencephalitis from other inflammatory brain diseases of young dogs.

From dog to man: the broad spectrum of inflammatory myopathies

The purpose of this review is to describe the various forms of inflammatory myopathy that occur spontaneously in dogs, and discuss the similarities and differences between inflammatory myopathy in dogs and humans. Some interesting muscle-specific autoantigens have recently been discovered in canine autoimmune myositis, and they are associated with specific forms of inflammatory myopathy. These autoantigens may now be investigated in humans. Furthermore, the association of distinct inflammatory myopathies with certain breeds of dogs point to important genetic components of inflammatory myopathy that can now be studied using dogs as both parallel disorders and animal models. Other canine myositides, associated with infectious and histiocytic diseases, may also be relevant to similar human disorders.

Expression of major histocompatibility complex class I and class II antigens in canine masticatory muscle myositis

Studies in human immune-mediated inflammatory myopathies have documented expression of major histocompatibility complex class I (MHC class I) and class II (MHC class II) antigens on muscle fiber membranes in the presence or absence of cellular infiltration. Here we evaluate the presence and distribution of these antigens in canine masticatory muscle myositis, an immune-mediated inflammatory myopathy. Twelve samples of temporalis and masseter muscles from dogs with a clinical diagnosis of canine masticatory muscle myositis were examined by immunohistochemistry and double-immunofluorescence confocal microscopy. MHC class I and class II antigens were expressed in muscle fibers independent of inflammatory cell infiltration. Furthermore MHC class I and class II antigens were expressed on the sarcolemma and co-localized with dystrophin. Our results suggest that MHC class I and class II expression in canine masticatory muscle myositis may play a role in the initiation and maintenance of the pathological condition, rather than just a consequence of a preceding local inflammation.

MAGNETIC RESONANCE IMAGING IN THE DIAGNOSIS OF CANINE INFLAMMATORY MYOPATHIES IN THREE DOGS

In humans affected with inflammatory myopathies, regions of altered signal intensity are found on magnetic resonance (MR) images of affected muscles. Although electromyography (EMG) is more practical for muscle disease evaluation, and a muscle biopsy is the only manner in which a definitive diagnosis can be made, MR imaging has proven useful if a specific anatomic localization is difficult to achieve. Three dogs with focal inflammatory myopathy diagnosed with the assistance of MR imaging are discussed and the findings are compared with those found in humans. MR images of the affected muscles in each dog were characterized by diffuse and poorly marginated abnormal signal on T1- and T2-weighted images. Marked enhancement was noted in these muscles after contrast medium administration. An inflammatory myopathy was confirmed histologically in all three dogs. A good association existed between the MR images and muscle inflammation identified histopathologically. MR imaging may be a useful adjunctive procedure for canine inflammatory myopathies.

Immunopathogenic pathways in canine inflammatory myopathies resemble human myositis

Progress in the treatment of inflammatory myopathies is impeded by the lack of suitable animal models. Inflammatory myopathies occur spontaneously in the dog, are a heterogeneous group of disorders, and are more common than in humans. Clinical signs of weakness and muscle atrophy are reliably present, and there are histological and immunohistological similarities to forms of human myositis. In this study, microarray technology followed by quantitative real-time PCR and immunohistochemistry on muscle biopsy sections was used to investigate gene expression in cases of canine inflammatory myopathies. Several genes involved with innate and adaptive immunity were highly upregulated including those that participate in macrophage and dendritic cell activation and migration, and antigen processing and presentation. Other genes including those that participate in B cell growth, development, migration and activation, immunoglobulin genes, genes in pro-inflammatory and anti-inflammatory pathways, and genes involved with tissue remodeling were upregulated. In previous reports utilizing microarray technology in human myositis, there was activation of similar pathways involved in the immune response. This study strengthens the argument that forms of canine myositis may be important animal models of human myositis and suggests useful biomarkers for therapeutic response using the dog in pre-clinical trials.

Sarcolemma-specific autoantibodies in canine inflammatory myopathy

Inflammatory myopathies (IM) are relatively common in dogs with an increased incidence in the Boxer and Newfoundland breeds. Here, we show that a high proportion of affected Boxers and Newfoundlands have circulating autoantibodies against unknown sarcolemma antigens, that are muscle-specific but not species specific. We further show that the autoantigen can be extracted from muscle membranes with non-ionic detergent, and that such detergent extracts can be used in a sensitive ELISA for detection and quantitation of antibodies. The relatively high incidence of IM with autoantibodies in selected breeds of dogs indicates a genetic predisposition for a particular form of IM. In these breeds, this form of IM could be diagnosed and monitored with a simple serum assay.

Evidence for MHC I–restricted CD8+ T-cell–mediated immunopathology in canine masticatory muscle myositis and polymyositis

Masticatory muscle myositis (MMM) is the most common inflammatory myopathy (IM) in dogs, associated with antibodies against myosin. To further elucidate the immunopathogenesis, we investigated muscles of 53 dogs with MMM, 32 dogs with polymyositis (PM), and 4 dogs suffering from both, with regard to the presence and location of CD4(+) and CD8(+)T cells, B cells, macrophages, major histocompatibility complex (MHC) class I and class II antigens, and autoantibodies. CD8(+)T cells were found in MMM (91%) and PM (75%), mostly paralleled (68% and 61%) by enhanced expression of MHC class I antigen on muscle fibers. CD8(+)T cells invading intact and neighboring necrotic muscle fibers were present in MMM (39%) and PM (42%). Dogs with MMM lacking intramuscular (26%) and circulating (36%) autoantibodies also had CD8(+) T-cell infiltrations and muscle-fiber lesions. Since MHC class I antigen and CD8(+) T cells were detected in the presence of CD4(+) T cells, regardless of antimuscular antibodies, we consider MMM and PM in the dog as a CD8(+) T-cell-mediated immunopathological disease that initiates muscle-fiber destruction and leads to production of myosin autoantibodies.

Dysphagia as the primary clinical abnormality in two dogs with inflammatory myopathy

Two adult Boxers were evaluated because of chronic dysphagia of several years' duration. Serum creatine kinase activity was high in both dogs, but other hematologic or serum biochemical abnormalities were not detected. Esophagraphy revealed abnormalities of the cricopharyngeal phase of swallowing in both dogs, and electromyography of the pharyngeal and laryngeal muscles revealed complex repetitive discharges, positive sharp waves, and fibrillation potentials characteristic of primary myopathy or neuropathy. Because of the severity of their condition, both dogs were euthanatized. Histologically, mixed-cell infiltrates were seen in sections of the masseter and thyropharyngeal muscles. Results of indirect immunofluorescence staining for proteins associated with dystrophic myopathy were unremarkable, except for decreased staining for integrin alpha7. A diagnosis of chronic inflammatory myopathy was made. The clinical importance of reduced staining for integrin alpha7 could not be determined but was considered to be a result of the myopathy.

Muscle regeneration, inflammation, and connective tissue expansion in canine inflammatory myopathy

Inflammatory myopathies (IMs) are relatively common in dogs, and canine IMs have many similarities to human IMs. The aim of this work was to analyze aspects of the pathogenesis of canine IM with an ultimate goal of establishing canine IM as a model for human IM. Muscle biopsies from 16 dogs with a histological diagnosis of IM were analyzed to determine degree of muscle regeneration, presence of eosinophils, expression of selected cytokines and chemokines, and extent of fibrosis. Regeneration, as shown by staining for developmental myosin heavy chain, was more extensive than evidenced with hematoxylin-eosin staining in most cases of canine IM. Expression of mRNA encoding transforming growth factor-beta (TGF-beta) and eotaxin 3 was upregulated in all cases evaluated. Eosinophils were abundant in most cases, and the connective tissue was variably expanded, as demonstrated by the distribution of the ubiquitous extracellular matrix proteins collagen VI and fibrillin. The extensive regeneration demonstrates that muscle may survive this adverse environment if inflammation and fibrosis can be stopped or reduced.

Canine and feline models of human inherited muscle diseases

Animal models are of immense importance for studying mechanisms of disease and testing new therapies, and rodents have been used extensively in the field of neuromuscular disorders. Mice and rats can be genetically manipulated to over-express or not express genes that are important to muscle function, and these animals can be available in large numbers for analysis. Other species, such as cats and dogs, cannot be manipulated in the same ways or be used in large numbers, but they have spontaneously occurring muscle diseases with clinical presentations more closely resembling those of the human disorders. Therefore, cats and dogs may become valuable as intermediate disease models. This review focuses on canine and feline models of human inherited muscle diseases with comparisons to rodent models and an emphasis on the muscular dystrophies.