Titin and ryanodine receptor autoantibodies in dogs with thymoma and late-onset myasthenia gravis

Successful Emergency Management of a Dog with Ventilator-Dependent Acquired Myasthenia Gravis with Immunoadsorption

A one-year-old, female intact Samoyed, 12.5 kg, was presented with coughing for 2 weeks, progressive appendicular and axial muscle weakness, megaesophagus and labored breathing for 5 days. There was no improvement with standard treatment. Acquired myasthenia gravis was suspected and the dog was referred with increasing dyspnea. At presentation, the dog showed a severely reduced general condition, was non-ambulatory and showed abdominal and severely labored breathing. A marked hypercapnia (PvCO2 = 90.1 mmHg) was present in venous blood gas analysis. The serum anti-acetylcholine receptor antibody test was consistent with acquired myasthenia gravis (2.1 nmol/L). The dog was anesthetized with propofol and mechanically ventilated with a Hamilton C1 ventilator. Immunoadsorption was performed with the COM.TEC® and ADAsorb® platforms and a LIGASORB® adsorber to eliminate anti-acetylcholine receptor antibodies. Local anticoagulation was performed with citrate. Treatment time for immunoadsorption was 1.5 h with a blood flow of 50 mL/min. A total plasma volume of 1.2 L was processed. Further medical treatment included intravenous fluid therapy, maropitant, esomeprazole, antibiotic therapy for aspiration pneumonia and neostigmine 0.04 mg/kg intramuscularly every 6 h for treatment of acquired myasthenia gravis. Mechanical ventilation was stopped after 12 h. A percutaneous gastric feeding tube was inserted under endoscopic control on day 2 for further medical treatment and nutrition. A second treatment with immunoadsorption was performed on day 3. Again, a total plasma volume of 1.2 L was processed. Immediately after this procedure, the dog regained muscle strength and was able to stand and to walk. After 6 days, the dog was discharged from the hospital. This is the first report of immunoadsorption for emergency management of a dog with acute-fulminant acquired myasthenia gravis. Immunoadsorption may be an additional option for emergency treatment in dogs with severe signs of acquired myasthenia gravis.

A scoping review of autoantibodies as biomarkers for canine autoimmune disease

Background

Autoantibody biomarkers are valuable tools used to diagnose and manage autoimmune diseases in dogs. However, prior publications have raised concerns over a lack of standardization and sufficient validation for the use of biomarkers in veterinary medicine.

Objectives

Systematically compile primary research on autoantibody biomarkers for autoimmune disease in dogs, summarize their methodological features, and evaluate their quality; synthesize data supporting their use into a resource for veterinarians and researchers.

Animals

Not used.

Methods

Five indices were searched to identify studies for evaluation: PubMed, CAB Abstracts, Web of Science, Agricola, and SCOPUS. Two independent reviewers (AET and ELC) screened titles and abstracts for exclusion criteria followed by full‐text review of remaining articles. Relevant studies were classified based on study objectives (biomarker, epitope, technique). Data on study characteristics and outcomes were synthesized in independent data tables for each classification.

Results

Ninety‐two studies qualified for final analysis (n = 49 biomarker, n = 9 epitope, and n = 34 technique studies). A high degree of heterogeneity in study characteristics and outcomes reporting was observed. Opportunities to strengthen future studies could include: (1) routine use of negative controls, (2) power analyses to inform sample sizes, (3) statistical analyses when appropriate, and (4) multiple detection techniques to confirm results.

Conclusions

These findings provide a resource that will allow veterinary clinicians to efficiently evaluate the evidence supporting the use of autoantibody biomarkers, along with the varied methodological approaches used in their development.

Acquired myasthenia gravis with concurrent polymyositis and myocarditis secondary to a thymoma in a dog

Background:

Canine thymomas are associated with multiple paraneoplastic syndromes, among which myasthenia gravis (MG) is the most common. Acquired MG is an autoimmune disease characterized by the presence of antibodies against acetylcholine receptors (ACHRs). ACHRs antibodies are the most commonly formed, but the production of antistriational antibodies binding to skeletal and cardiac muscle proteins has also been recorded both in humans and dogs. An association between the occurrence of antistriational antibodies and a severe form of myocarditis, giant cell myocarditis, has been described in humans.

Case Description:

A 4-year-old mixed-breed dog was referred because of 1 month history of exercise-induced weakness, hypersalivation, and regurgitation. The neurologic examination was indicative of a neuromuscular junction disease, and MG was suspected. A computed tomographic scan examination showed the presence of a megaoesophagus and a thymic mass. Serum antibodies against ACHRs confirmed the diagnosis of MG. Treatment with pyridostigmine was started, and the thymic mass was surgically excised, and a diagnosis of thymoma was confirmed by histology. 24 hours after surgery, the dog developed a third-degree atrioventricular block. Severe arrhythmia and increased troponin serum levels suggested myocarditis which rapidly led to cardiopulmonary arrest. Histopathologic examination of the heart, esophagus and diaphragm revealed a lymphocytic and macrophagic infiltration, consistent with myocarditis and polymyositis. Scattered rare giant multinucleated cells were also detected in the myocardium.

Conclusion:

To the author’s knowledge, this is the first report of thymoma-associated MG with concurrent polymyositis and giant cell-like myocarditis in a dog.

Clinical features and outcome of acquired myasthenia gravis in 94 dogs

Background

Factors known to be associated with outcome of acquired myasthenia gravis (MG) in dogs are limited.

Hypothesis/Objectives

Of dogs with MG, advancing age and comorbid neoplasia are associated with poor long‐term prognosis and low rates of remission.

Animals

Ninety‐four client‐owned dogs with MG diagnosed by acetylcholine receptor antibody (AChR Ab) assay between 2001 and 2019 from a university clinic and 3 private clinics in the United States.

Methods

Cases were retrospectively evaluated and data were collected to determine clinical signs, treatment, and response to therapy defined by means of a clinical scoring rubric. Immunological remission was defined as a return of the AChR Ab concentration to <0.6 nmol/L. Multivariable binary logistic regression analysis was used to identify clinical criteria predicting remission.

Results

An anticholinesterase drug was used to treat 90/94 (96%) dogs, which in 63/94 (67%) was the sole treatment; other drugs included immune modulators. Clinical remission (lack of clinical signs ≥4 weeks after treatment cessation) was observed in 29 (31% [95% confidence interval (CI): 22.4‐40.8%]) dogs, clinical response (lack of clinical signs on treatment) in 14 (15% [95% CI: 9.0‐23.6%]) dogs, clinical improvement (on treatment) in 24 (26% [95% CI: 17.8‐35.2%]) dogs, and no clinical improvement in 27 (29% [95% CI: 20.5‐38.6%]) dogs. Immunological remission was observed in 27/46 (59%) dogs, with clinical remission in all 27. Younger age (P = .04) and comorbid endocrine disease (P = .04) were associated with clinical remission. Initial AChR Ab concentration (P = .02) and regurgitation (P = .04) were negatively associated with clinical remission.

Conclusions and Clinical Importance

Clinical remission in MG is less likely in older dogs and dogs presenting with regurgitation or high initial AChR Ab concentration, but more likely in younger dogs and dogs with comorbid endocrine disease.

Classification of myasthenia gravis and congenital myasthenic syndromes in dogs and cats

Myasthenia, a syndrome of impaired neuromuscular transmission, occurs as either an acquired or congenital condition. Myasthenia gravis (MG) is an acquired autoimmune disorder with autoantibodies against the neuromuscular junction (NMJ) of skeletal muscle whereas congenital myasthenic syndromes (CMSs) are a clinically heterogeneous group of genetic disorders affecting the NMJ with a young age of onset. Both conditions are diseases for which recognition is important with regard to treatment and outcome. We review the published literature on MG and CMSs in dogs and cats, and by comparison with published classification used in humans, propose a classification system for MG and CMSs in dogs and cats. Myasthenia gravis is first classified based on focal, generalized, or acute fulminating presentation. It then is subclassified according to the autoimmune disease mechanism or seronegativity. Autoimmune disease mechanism relates to the presence or absence of a thymoma, or administration of thiourylene medication in cats. Congenital myasthenic syndromes are classified according to the affected NMJ component, the mechanism of the defect of neuromuscular transmission, the affected protein, and ultimately the mutated gene responsible. In proposing this categorization of MG and CMSs, we hope to aid recognition of the disease groups for both conditions, as well as guide treatment, refine prognosis, and provide a framework for additional studies of these conditions.

The Dog Model in the Spotlight: Legacy of a Trustful Cooperation

Dogs have long been used as a biomedical model system and in particular as a preclinical proof of concept for innovative therapies before translation to humans. A recent example of the utility of this animal model is the promising myotubularin gene delivery in boys affected by X-linked centronuclear myopathy after successful systemic, long-term efficient gene therapy in Labrador retrievers. Mostly, this is due to unique features that make dogs an optimal system. The continuous emergence of spontaneous inherited disorders enables the identification of reliable complementary molecular models for human neuromuscular disorders (NMDs). Dogs’ characteristics including size, lifespan and unprecedented medical care level allow a comprehensive longitudinal description of diseases. Moreover, the highly similar pathogenic mechanisms with human patients yield to translational robustness. Finally, interindividual phenotypic heterogeneity between dogs helps identifying modifiers and anticipates precision medicine issues.

This review article summarizes the present list of molecularly characterized dog models for NMDs and provides an exhaustive list of the clinical and paraclinical assays that have been developed. This toolbox offers scientists a sensitive and reliable system to thoroughly evaluate neuromuscular function, as well as efficiency and safety of innovative therapies targeting these NMDs. This review also contextualizes the model by highlighting its unique genetic value, shaped by the long-term coevolution of humans and domesticated dogs. Because the dog is one of the most protected research animal models, there is considerable opposition to include it in preclinical projects, posing a threat to the use of this model. We thus discuss ethical issues, emphasizing that unlike many other models, the dog also benefits from its contribution to comparative biomedical research with a drastic reduction in the prevalence of morbid alleles in the breeding stock and an improvement in medical care.

Long-term outcome of cats with acquired myasthenia gravis without evidence of a cranial mediastinal mass

Background

Acquired myasthenia gravis (AMG) is increasingly recognized in cats, yet information regarding the natural history of the disease, treatment, and outcome including occurrence of immune and spontaneous remission remains limited.

Objective

To determine the long‐term outcome of cats with AMG without evidence of a cranial mediastinal mass (CMM).

Animals

Eight cats diagnosed with AMG without evidence of a CMM.

Methods

Retrospective case series. The medical records of cats diagnosed with AMG between 2005 and 2018 from 2 veterinary referral hospitals were reviewed for inclusion. Inclusion criteria consisted of a diagnosis of AMG, thoracic imaging, serum biochemistry including measurement of creatine kinase, and a CBC. Exclusion criteria were the presence of an identifiable CMM, or administration of methimazole or carbimazole.

Results

All cats had an excellent long‐term outcome, achieving immune remission within 6 months of diagnosis, including 4 cats that did not receive any treatment and whose natural course of disease involved spontaneous remission. Clinical presentation was heterogeneous, and skeletal muscle weakness and fatigability induced or exacerbated by the wheelbarrow exercise stress test were the most consistent abnormalities associated with AMG.

Conclusion and Clinical Importance

Cats diagnosed with AMG without evidence a CMM have a favorable outcome and frequently achieve immune remission. Moreover, the natural history of AMG in cats includes spontaneous remission when there is no evidence of a CMM. Attempting to rule out the presence of a CMM therefore refines prognosis, and treatment is not always necessary in this disease population.

Introducing Autoimmunity at the Synapse by a Novel Animal Model of Experimental Autoimmune Myasthenia Gravis

The neuromuscular junction (NMJ) is a peripheral synapse between motor neurons and skeletal muscle fibers that controls muscle contraction. The NMJ is the target of various disorders including myasthenia gravis (MG), an autoimmune disease in which auto-antibodies (auto-Abs) attack the synapse, and thus cause muscle weakness in patients. There are multiple auto-Abs in the MG patient sera, but not all the Abs are proven to be pathogenic, which increases the difficulties in clinical diagnoses and treatments. To establish the causative roles of auto-Abs in MG pathogenesis, the experimental autoimmune MG (EAMG) induced by the active immunization of auto-antigens (auto-Ags) or the passive transfer of auto-Abs is required. These models simulate many features of the human disease. To date, there are three kinds of EAMG models reported, of which AChR-EAMG and MuSK-EAMG are well characterized, while the recent LRP4-EAMG is much less studied. Here, we report a current summary of LRP4-EAMG and its pathogenic mechanisms. The features of LRP4-EAMG are more similar to those of AChR-EAMG, indicating a similar clinical treatment for LRP4- and AChR-positive MG patients, compared to MuSK-positive MG patients.

Evaluation of coexisting polymyositis in feline myasthenia gravis: A case series

Acquired myasthenia gravis (MG) is relatively uncommon in cats. In humans, MG may be associated with other immune-mediated disorders, in particular polymyositis (PM). In this study, we described in-depth electrodiagnostic findings and pathological changes in muscles of cats diagnosed with MG, and assessed the presence of concurrent PM. Six cats with confirmed acetylcholine receptor antibody seropositive MG, and two suspected cases with clinical signs and electrophysiological changes consistent with MG, were reviewed. All animals presented with severe typical signs of generalized weakness and/or fatigability, resembling late-onset MG in humans, in addition to regurgitation. Five cats presented a cranial mediastinal mass, with 3 confirmed as thymoma. Repetitive nerve stimulation revealed a decrement of the compound muscle action potential in all tested cases, starting from low frequencies of stimulation. Serum creatine kinase activity was increased in 6/8 cats. Muscle biopsies performed in 5 cats revealed varying degrees of mixed mononuclear cell infiltrates, positive for the leukocyte markers CD3/CD4/CD8 and CD11b. Further MHC-1/C5b-9 positive sarcolemmal deposits were identified in all tested cases, with or without thymoma. This study documents an association of MG and PM in cats, and provides further support for feline MG as a relevant animal model of human MG.

Thymoma related myasthenia gravis in humans and potential animal models

Thymoma-associated Myasthenia gravis (TAMG) is one of the anti-acetylcholine receptor MG (AChR-MG) subtypes. The clinico-pathological features of TAMG and its pathogenesis are described here in comparison with pathogenetic models suggested for the more common non-thymoma AChR-MG subtypes, early onset MG and late onset MG. Emphasis is put on the role of abnormal intratumorous T cell selection and activation, lack of intratumorous myoid cells and regulatory T cells as well as deficient expression of the autoimmune regulator (AIRE) by neoplastic thymic epithelial cells. We review spontaneous and genetically engineered thymoma models in a spectrum of animals and the extensive clinical and immunological overlap between canine, feline and human TAMG. Finally, limitations and perspectives of the transplantation of human and murine thymoma tissue into nude mice, as potential models for TAMG, are addressed.

In silico study of potential autoimmune threats from rotavirus infection

Rotavirus, the major cause of infantile nonbacterial diarrhea, was found to be associated with development of diabetes-associated auto-antibodies. In our study we tried to find out further potential autoimmune threats of this virus using bioinformatics approach. We took rotaviral proteins to study similarity with Homo sapiens proteome and found most conserved structural protein VP6 matches at two regions with ryanodine receptor, an autoimmune target associated with myasthenia gravis. Myasthenia gravis, a chronic neurodegenerative autoimmune disorder with no typical known reason, is characterized by fluctuating muscle weakness which is typically enhanced during muscular effort. Affected patients generate auto antibodies against mainly acetyl choline receptor and sarcoplasmic reticulum calcium-release channel protein ryanodine receptor. Further, we observed that two regions which matched with ryanodine receptor remain conserved in all circulating rotaviral strains and showed significant antigenecity with respect to myasthenia gravis associated HLA haplotypes. Overall, our study detected rotaviral VP6 as a potential threat for myasthenia gravis and enlighten an area of virus associated autoimmune research.

Myasthenia gravis in dogs with an emphasis on treatment and critical care management

OBJECTIVE

To review the human and veterinary literature on the pathophysiology of myasthenia gravis (MG) and describe treatment options for clinical use in people and animals.

DATA SOURCES

Human and veterinary clinical reports, studies and reviews, textbooks, and recent research findings in MG from 1996 present, with a focus on treatment and patient management.

HUMAN DATA SYNTHESIS

MG is a well-described condition in people with new research and treatment options available. Many of the newest therapeutic options available in veterinary medicine for MG are based on current strategies used in people with this condition. Seronegative MG is well described in people and provides insight to clinical cases encountered in veterinary medicine when the index of suspicion is high though serologic tests are negative.

VETERINARY DATA SYNTHESIS

Previous studies in veterinary medicine focused on the use of acetylcholinesterase inhibitors as the main form of treatment in canine MG. Recent studies, mainly case series and case reports, emphasize the use of immunomodulatory treatments as an alternative for long-term treatment. However, there are no randomized, controlled studies on treatment with immunomodulatory therapy for MG in dogs available to assess the efficacy of this treatment strategy.

CONCLUSIONS

Although early recognition of clinical signs is most important in the outcome of patients with MG, further understanding the pathophysiology of MG may lead to earlier diagnosis and novel treatment strategies. The discovery of additional autoantibodies against striated muscle proteins in dogs, should enhance our understanding of diseases affecting the neuromuscular junction. In addition, clinical data for canine MG could be applied to other autoimmune disorders.

Routine and specialized laboratory testing for the diagnosis of neuromuscular diseases in dogs and cats

The diagnosis of neuromuscular diseases can be challenging. The first step is recognition that the disease involves the neuromuscular system (muscle, neuromuscular junction, peripheral nerve, and ventral horn cells of the spinal cord). Many neuromuscular diseases share clinical signs and cannot be distinguished based on clinical examination. Routine laboratory screening, including a CBC, biochemical profile, and urinalysis, can identify some of the most common systemic abnormalities that cause muscle weakness and myalgia, such as hypo- and hyperglycemia, electrolyte disorders, or thyroid abnormalities, and may suggest a specific diagnosis, such as diabetes mellitus, hypo- or hyperadrenocorticism, renal failure, or hypothyroidism. Increased creatine kinase activity, increased cardiac troponin I concentration, and myoglobinuria are useful in detecting skeletal and cardiac muscle damage. Identification of acetylcholine receptor antibodies is diagnostic for acquired myasthenia gravis. For primary muscle or peripheral nerve diseases, tissue biopsy is the most direct way to determine specific pathology, correctly classify the disease, and determine the course of additional laboratory testing. For example, inflammatory, necrotizing, dystrophic, metabolic, or congenital myopathies require different laboratory testing procedures for further characterization. Many neuromuscular diseases are inherited or breed-associated, and DNA-based tests may already be established or may be feasible to develop after the disorder has been accurately characterized. This review focuses on both routine and specialized laboratory testing necessary to reach a definitive diagnosis and determine an accurate prognosis for neuromuscular diseases.

Autoimmune myasthenia gravis in a ferret

CASE DESCRIPTION

A 7-month-old neutered male ferret was evaluated for episodic pelvic limb weakness of 2 weeks' duration.

CLINICAL FINDINGS

Neurologic examination revealed flaccid tetraparesis with decreased spinal reflexes suggestive of a neuromuscular disease. Results of hematologic and CSF analyses, thoracic radiography, and abdominal ultrasonography were unremarkable. Electrodiagnostic testing revealed subtle spontaneous activity localized to pelvic limb interosseous muscles, unremarkable motor nerve conduction velocities, and lower than typical compound muscle action potential (CMAP) amplitude for tibial nerve stimulation only. A severe decremental response of the CMAP was detected with repetitive nerve stimulation (45.5% at the third ulnar nerve). An esophagogram revealed mild megaesophagus. Intravenous neostigmine methylsulfate administration resulted in immediate resolution of muscle weakness. Cross-reacting anti-acetylcholine receptor (AChR) antibodies were detected in serum (0.35 nmol/L) by use of a canine- and feline-specific muscle extract. Clinical signs and ancillary test results were diagnostic of acquired myasthenia gravis.

TREATMENT AND OUTCOME

Pyridostigmine bromide was administered (1 mg/kg [0.45 mg/lb], PO, q 8 h), resulting in complete remission of clinical signs. However, 1 month after the diagnosis, the ferret was euthanized because of recurrence of weakness despite anticholinesterase treatment.

CLINICAL RELEVANCE

To the authors' knowledge, this is the first report of acquired myasthenia gravis in a ferret and the first identification of anti-AChR antibodies in this species. Autoimmune myasthenia gravis should be considered in ferrets when weakness and flaccid paresis suggest a neuromuscular disease. Electrodiagnostic testing, anticholinesterase challenge, and AChR antibody titer determination were helpful for diagnosis of this condition.

A Screening for the Occurrence of Autoreactive Antibodies in Sera of Pregnant and Non-pregnant Bitches

Sera of healthy pregnant (group I, n = 11) and non-pregnant (group II, n = 11) bitches were screened for autoantibodies (AAb). In both groups, blood samples were drawn every fifth day between days 5 and 55 after mating. Serum was analysed via indirect immunofluorescence (IIF) with the Canine ANA HEp-2 Screening Kit. In all animals, anticytoplasmic AAb were detected. Utilizing primate-heart substrate slides AAb against contractile proteins of the cytoplasm could be observed. The predominating fluorescence pattern in pregnant animals resembled above all desmin, which was proven via Western blot. The sera were then pre-incubated with tropomyosin, actin, vimentin, vinculin and keratin solutions, and assessed on HEp-2 slides and on human and canine fibroblasts as well. The latter substrate was used to verify whether the detected Ab were in fact AAb. Utilizing tropomyosin, revealed elimination of the cytoplasmic fluorescences on all three substrates. It is therefore assumed, that in sera of healthy dogs, AAb against contractile structure proteins of the cytoplasm are present regularly. The majority of pregnant bitches presented with higher end-point titres (EPT), than to be found in non-pregnant dogs. AAb against desmin played the key role in those patterns. In addition, sera were screened for thyroid specific AAb, namely thyroglobulin, thyroid peroxidase (TPO), T3 and T4, and for AAb against insulin by ELISA or Western blot (TPO). Only in two of the pregnant bitches a weak positive reaction (1:100) for T3-AAb was detected.

Uveodermatologic (VKH-like) syndrome in American Akita dogs is associated with an increased frequency of DQA1*00201

The Akita breed of dog is affected by a number of distinct immune-mediated diseases, including thyroiditis, sebaceous adenitis, pemphigus foliaceus, uveitis, polyarthritis, myasthenia gravis, and uveodermatologic (UV) syndrome. UV syndrome is manifested by progressive uveitis and depigmenting dermatitis that closely resembles the human Vogt - Koyanagi - Harada syndrome. This study examined the allelic diversity of the three DLA class II loci (DRB1, DQA1, and DQB1) in the American Akita dog, and the relationship of specific DLA class II alleles to the UV. Low allelic variation was demonstrated within genes of DLA class II. American Akita dogs possessed six of the reported 16 DQA1 alleles, but only eight of 61 reported alleles in DRB1 and nine of 47 reported alleles in DQB1. Almost one-half of American Akita dogs were homozygous for a single allele at DQA1 and up to a quarter at DRB1 and DQB1. DLA-DQA1*00201 was associated with a significantly higher relative risk (RR = 15.3) or odds ratio (OR = 15.99) for UV syndrome than other DLA class II alleles. No significant association was noted with haplotypes of DRB1, DQB1, and DQA1 alleles; DRB1*03201-DQA1*00201 trended toward significance. This study confirmed loss of DLA genetic diversity in the American Akita dog in common with other pure breeds of dog and suggested a role for certain DLA class II gene alleles in the pathogenesis of UV.

Myasthenia Gravis and Hypothyroidism in a Dog With Meningomyelitis

A 12-year-old, spayed female miniature poodle was evaluated because of a 4-day history of paraparesis, dysuria, and tenesmus. Neurological assessment suggested peripheral nervous system dysfunction, predominantly pelvic limb weakness with a possible concurrent sixth lumbar (L6) to second sacral (S2) myelopathy. Further studies supported the diagnoses of myasthenia gravis, hypothyroidism, and meningomyelitis. To the authors’ knowledge, this is the first reported case of concurrent myasthenia gravis and meningomyelitis in the dog. It was unclear whether the identified conditions evolved from a shared etiopathogenesis or were merely coincidental.

Thymoma in a dog with a part of granular cell proliferation and concurrent lymphoma cells

A 12-year-old male Shiba dog showed anemia and the swelling of systemic lymph nodes. X-ray and post mortal examinations revealed a anterior mediastinal mass. Histologically, the tumor mass consisted of four different elements; cord-like proliferation of cuboidal epithelial cells, tubular or cystic structures lined with ciliated epithelial cells, proliferation of large round-shaped epithelial cells with PAS-slightly positive granular cytoplasm, and diffuse proliferation of neoplastic lymphocytes. Epithelial cells in cord-like or cystic structures were strongly positive for cytokeratin. Granular or foamy cells were negative for all markers examined and had myelin-like bodies in the cytoplasm by electron microscopy. The neoplastic lymphocytes in the tumor mass were considered being derived from concurrent multicentric lymphoma. Based on these findings, the present case was diagnosed as thymoma with a part of granular cell proliferation and concurrent lymphoma cells.

Thymoma and multiple thymic cysts in a dog with acquired myasthenia gravis

An anterior mediastinal cystic lesion in an 11-year-old mongrel dog was examined. The dog showed dysbasia and vomiting due to megaoesophagus, and anterior mediastinal round mass lesion, approximately 35 mm in diameter, was found by X ray. Based on clinical examinations, the dog was diagnosed as acquired myasthenia gravis and was successfully controlled by anticholinesterase treatment for approximately 4 months. The dog died of thermic stroke and was necropsied. Grossly, fatty tissues with cysts containing yellowish fluid and white nodules were found in the anterior mediastinal area. Histopathologically, multiple cysts, neoplastic tissues, and atrophic thymus were found within the examined tissues. The cysts were lined by thin wall consisting of ciliated long cuboidal and non-ciliated round cells and were filled with eosinophilic colloidal fluid. Some extended cysts contained neoplastic foci within their lumen and walls. The neoplastic tissues consisted of mixed population of large epithelial cells with abundant clear cytoplasm and large oval nuclei, and lymphocytes. Immunohistochemically, proliferating epithelial cells were intensely positive for keratin and cytokeratin, and more than half number of infiltrating lymphocytes were intensely positive for CD3 suggesting T cells. All these findings indicate the neoplastic lesion is thymoma and multiple cysts are considered as thymic or brachial cleft cysts.

Titin and ryanodine receptor epitopes are expressed in cortical thymoma along with costimulatory molecules

Cortical-type thymomas are associated with myasthenia gravis (MG) in 50% of the cases. MG is caused by antibodies against the acetylcholine receptors (AChR), but additional non-AChR muscle autoantibodies such as those against titin and ryanodine receptor (RyR) are found in up to 95% of MG patients with thymoma. To elucidate the induction of non-AChR autoantibodies in thymoma-associated MG, we studied cortical-type thymomas from seven thymoma MG patients, and sera from six of them. All six had titin antibodies, and four had RyR antibodies. Titin and RyR epitopes were co-expressed along with LFA3 and B7 (BB1) costimulatory molecules on thymoma antigen-presenting cells (APC) in all thymomas. In normal thymus, the staining by anti-titin, anti-RyR, anti-LFA3, and anti-BB1 antibodies was weak and occurred exclusively in the medulla and perivascularly. Our results indicate a primary autosensitization against titin and RyR antigens inside the thymoma. In MG-associated thymoma, the mechanisms involved in the initial autosensitization against titin and RyR are probably similar to those implicated in the autosensitization against AChR. In all cases, there is an overexpression of muscle-like epitopes and costimulatory molecules indicating that the T-cell autoimmunization is actively promoted by the pathogenic microenvironment inside the thymoma.

Myasthenia gravis and disorders of neuromuscular transmission

Myasthenia gravis is a disorder of neuromuscular transmission that occurs in congenital and acquired autoimmune forms. Acquired myasthenia gravis is probably the most common neuromuscular disorder in dogs that can be diagnosed and treated. An early, accurate diagnosis and appropriate therapy is of utmost importance to a good clinical outcome in this disorder. This article focuses on the diagnosis and treatment of acquired myasthenia gravis in dogs and cats with brief discussions of other disorders of neuromuscular transmission, including congenital myasthenia gravis, tick paralysis, botulism, and organophosphate intoxication.