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.     

Clinical remission following plasmapheresis and corticosteroid treatment in a dog with acquired myasthenia gravis

A 7-year-old sexually intact male Labrador Retriever with regurgitation and generalized muscular weakness resulting from acquired myasthenia gravis received 2 plasmapheresis treatments in combination with corticosteroid treatment. Plasmapheresis was performed in an attempt to rapidly lower serum acetylcholine receptor binding antibody (AChR Ab) concentration. Seven days after the second plasmapheresis treatment, the dog's muscular strength was normal, which coincided with a 70% decrease in serum AChR Ab concentration. Because the dog also received corticosteroids, it is impossible to determine how much of the clinical improvement resulted from plasmapheresis.     

Focal myasthenia gravis in a dog.

A 10-month-old American cocker spaniel was evaluated for megaesophagus, aspiration pneumonia, but no appendicular muscle weakness. During hospitalization, weakness of the facial muscles developed, this resolved with anticholinesterase administration. Serum antibodies against acetylcholine receptors were documented, confirming the diagnosis of focal myasthenia gravis. Diagnosis, management, and medical treatment are discussed.     

Autoimmune myasthenia gravis and dysautonomia in a dog

A two-year-old male entire border collie dog was evaluated for a short history of mixed bowel diarrhoea, coughing, vomiting and stranguria. Physical examination revealed dyspnoea with increased ventral lung sounds and a flaccidly distended bladder. Neurological examination revealed poor pupillary light reflexes, an absent gag reflex and a poor anal tone. Thoracic radiography was consistent with megaoesophagus and aspiration pneumonia. Clinicopathological testing revealed an elevated muscular nicotinic acetylcholine receptor antibody titre. The dog was euthanased because of clinical deterioration. Cerebrospinal fluid (CSF) collected immediately post-mortem revealed macrophagic pleocytosis. Post-mortem histopathological examination was consistent with dysautonomia. This is the first report of coexisting autoimmune myasthenia gravis and dysautonomia in a non-human species. The concomitant diseases may suggest a common immunopathological aetiology.     

Acquired myasthenia gravis associated with oral sarcoma in a dog

Acquired myasthenia gravis is a common neuromuscular disorder resulting from autoantibody directed against the post-synaptic acetylcholine nicotinic receptors in skeletal muscle. Myasthenia gravis has been reported previously as a paraneoplastic syndrome. This case report presents myasthenia gravis secondary to an oral sarcoma in a juvenile Mastiffdog.     

Acquired myasthenia gravis associated with a non-invasive thymic carcinoma in a dog

An 8 1/2-year-old neutered male Beagle was diagnosed with acquired myasthenia gravis associated with a non-invasive thymic carcinoma. The thymic mass was surgically excised and the dog was treated with pyridostigmine, prednisolone and azathioprine. Serial acetylcholine receptor antibody titres were increased initially but slowly declined to normal values over a period of 24 weeks. Improved exercise tolerance was seen following therapy, however, oesophageal dysfunction persisted. The dog was euthanased 26 weeks after initial presentation due to a complicating illness. A necropsy showed no regrowth or metastasis of the thymic carcinoma.     

Acquired myasthenia gravis and cholangiocellular carcinoma in a dog

Acquired myasthenia gravis and cholangiocellular carcinoma were diagnosed in a 7-year-old English Setter referred because of forelimb lameness, exercise-induced weakness, and fever. Three months earlier, the dog had had a pleuropulmonary infection caused by a Fusobacterium sp. The concurrent development of myasthenia gravis and cholangiocellular carcinoma in this dog may be explained by a paraneoplastic syndrome, although it is unproven. The cholangiocellular carcinoma may have possessed an acetylcholine receptor-like antigen on the tumor surface, which induced autoantibodies to cross-react with acetylcholine receptors at the neuromuscular junction.     

Metastatic thymoma and acquired generalized myasthenia gravis in a beagle

A 16-year-old, spayed female beagle was diagnosed with metastatic thymoma causing a probable paraneoplastic syndrome of generalized acquired myasthenia gravis. Anticholinesterase treatment was initiated; however, 5 days later the dog died.     

Treatment of acquired myasthenia gravis associated with thymoma in two dogs

Two cases of myasthenia gravis associated with thymoma are reported. Both were female German shepherd dogs and the thymoma was surgically resected. Aspiration pneumonia secondary to persistent megaoesophagus was a complication in both cases. The myasthenia gravis did not resolve, but there was a more satisfactory control of clinical signs with anticholinesterase treatment. Corticosteroid therapy was used in one case, but the resulting polydipsia increased the incidence of regurgitation, resulting in recurrent episodes of aspiration pneumonia.     

Speed of reversal of vecuronium neuromuscular block with different doses of neostigmine in anesthetized dogs

Objectives

Neostigmine is routinely used to reverse non-depolarizing neuromuscular block. Given its indirect mechanism, a plateau may exist whereby increasing doses of neostigmine do not result in clinical benefit. This study was designed to measure the speed of reversal of vecuronium-induced neuromuscular block in isoflurane-anesthetized dogs after the administration of three doses of neostigmine as used in clinical practice.

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.     

Intravenous administration of 9-aminocamptothecin to dogs with lymphoma

A colloidal dispersion formulation of 9‐aminocamptothecin (9‐AC) was administered intravenously to 10 dogs with previously untreated, spontaneously occurring, multicentric lymphoma. The dogs received a 72‐h infusion of 9‐AC at a rate of 46.5–51.25 µg m^?2 h^?1 (total dose range 3.35–3.69 mg m^?2). This dose range was associated with myelosuppression, consisting principally of neutropenia with a nadir at 7 days following the start of infusion. Neutropenia and thrombocytopenia were the most common toxicoses and are most likely to be dose‐limiting toxicities; low‐grade gastrointestinal signs were rarely seen. Concentrations of 9‐AC lactone, as well as clinical toxicities, compare favourably with those found in humans. Tumour responses were seen in all treated dogs. Response to other chemotherapy, following cessation of 9‐AC treatment, was not obviously compromised even in dogs clinically resistant to 9‐AC. 9‐AC is a novel treatment drug for canine lymphoma, which appears to show great promise.     

Restenosis after balloon valvuloplasty in a dog with pulmonary stenosis

A two-month-old female Chihuahua was diagnosed as severe pulmonary valvular stenosis (PS). Although balloon valvuloplasty (BV) was successfully performed, restenosis was observed 19 months after the procedure. Euthanasia was chosen due to low output syndrome during the surgical repair attempted when the dog was 5 years old. Postmortem examination revealed markedly thickened pulmonary valve due to the increase of extracellular matrix which might be produced by increased α smooth muscle actin-positive myofibroblasts. The thickening of the valve was associated with restriction of the valve’s motion, resulting in restenosis in the present case. This is the first case report documented histopathological and immunohistochemical findings of the restenotic pulmonary valve in dogs with PS after BV.     

Acquired myasthenia gravis in a cat with thymoma

A 4-year-old castrated Abyssinian cat was evaluated for profound neuromuscular weakness. Results of electromyography and repetitive nerve stimulation tests were normal. Thoracic radiography revealed a cranial mediastinal mass, which was excised and identified as a thymoma. Serum acetylcholine receptor antibodies were detected at high concentration, supporting a diagnosis of acquired myasthenia gravis. Clinical signs of disease responded to treatment with pyridostigmine and corticosteroids.     

Rebound hyperkalemia in a dog with albuterol toxicosis after cessation of potassium supplementation

Objective

To describe the presentation of rebound hyperkalemia as a delayed side effect of albuterol toxicity in a dog.

Case Summary

A 3-year-old female neutered mixed-breed dog was presented for albuterol toxicosis that led to a severe hypokalemia, hyperlactatemia, and hyperglycemia. The dog also experienced sinus tachycardia and generalized weakness. Treatment was instituted with intravenous fluid therapy and potassium supplementation, and the dog was monitored with a continuous electrocardiogram. Resolution of hypokalemia was documented 12 hours after initial presentation, at which time fluid therapy and potassium supplementation were discontinued. There were no further periods of sinus tachycardia, but instead the dog developed ventricular ectopy with rapid couplets (instantaneous rates of 300/min). An echocardiogram revealed normal cardiac size and function. Twenty-four hours after presentation, the patient developed severe hyperkalemia, despite discontinuation of fluids and potassium supplementation for 12 hours. Serial venous and urinary electrolytes were performed for determination of the fractional excretion of electrolytes. These data confirmed rebound hyperkalemia (7.0 mmol/L), consistent with a markedly increased fractional excretion of potassium, and secondary to the release of potassium from inside the cells. Fluid therapy with dextrose supplementation was provided until 36 hours postpresentation. The hyperkalemia resolved, and the dog was discharged after 44 hours of hospitalization.

New or Unique Information Provided

This case documents rebound hyperkalemia following treatment of albuterol toxicosis in a dog. This case highlights the importance of understanding the distribution of total body potassium when treating serum hypokalemia. Transcellular shifts of potassium, as in the case of albuterol toxicosis, can lead to rebound hyperkalemia even after discontinuation of potassium supplementation. This case further explores the utility of fractional excretion of electrolytes in elucidating the etiology and management of electrolyte disturbances.     

Thymoma removal in a cat with acquired myasthenia gravis: a case report and literature review of anesthetic techniques

History and presentation A 12 year old, 4.2 kg, domestic long hair, castrated male cat was presented with regurgitation, inability to retract the claws, general weakness, cervical ventroflexion and weight loss. A thymic mass was evident on radiographs. Acetylcholine receptor antibody titer was positive for acquired myasthenia gravis (MG). Thymectomy via midline sternotomy was scheduled. Anesthetic management Oxymorphone and atropine were administered subcutaneously as premedication, and anesthesia was induced with etomidate and diazepam given intravenously to effect. The cat’s trachea was intubated and anesthesia was maintained with isoflurane in oxygen, and continuous infusions of remifentanil and ketamine. Epidural analgesia with preservative‐free morphine was administered prior to surgery. Postoperative analgesia was provided by oxymorphone subcutaneously, interpleural bupivacaine, and fentanyl infusion. Postoperative complications included airway obstruction, hypoxemia and hypercapnia. Follow‐up The cat was discharged 3 days after surgery. Discharge medications included pyridostigmine and prednisone. Nine days after surgery, the cat had a significant increase in its activity level, and medications were discontinued. Histopathologically, the mass was consistent with a thymoma. Approximately 6 weeks later the cat became weak again and pyridostigmine and prednisone administration was resumed. Conclusion The perioperative management of patients with MG for transsternal thymectomy is a complex task. The increased potential for respiratory compromise requires the anesthesiologist to be familiar with the underlying disease state, and the interaction of anesthetic and non‐anesthetic drugs with MG. Careful monitoring of ventilation and oxygenation is indicated postoperatively.     

Nasal infection with Scedosporium apiospermum in a dog

CASE HISTORY: A 2-year-old female Siberian Husky was presented with a 6-month history of sneezing and mucous discharge from the right nostril.

CLINICAL FINDINGS: Reduced airflow through the right nostril was evident. Radiographs showed subtle loss of detail of turbinates within the right nasal chamber. Rhinoscopy revealed swollen and erythematous turbinates and a white mass within the caudal aspect of the right nasal cavity. Histopathologically, there was a heavy mixed inflammatory infiltrate in the submus- cosa of the right turbinate, and the presence of fungal hyphae and spores in the white mass. A heavy growth of Scedosporium apiospermum was cultured from the mass.

DIAGNOSIS: Chronic rhinitis of the right nasal cavity and infection with S. apiospermum.

CLINICAL RELEVANCE: This is the first reported case of S. apiospermum isolated from the nasal cavity of a dog in New Zealand. Fungal culture is necessary to differentiate this fungus from Aspergillus spp.     

Use of mycophenolate mofetil as a rescue agent in the treatment of severe generalized myasthenia gravis in three dogs

Objective – To describe the use of IV and oral mycophenolate mofetil (MMF) as adjunctive therapy in 3 dogs with severe generalized myasthenia gravis.
Case Series Summary – Three dogs suffering from severe generalized myasthenia gravis as confirmed by acetylcholine antibody titers were treated with MMF as part of their treatment regimens. All 3 dogs had radiographic evidence of megaesophagus and suffered from severe regurgitation. Each dog was initially treated with pyridostigmine and supportive agents. When clinical remission was not achieved, IV MMF was administered to all dogs. Signs of clinical remission were apparent within 48 hours and all dogs were later maintained on oral MMF following resolution of regurgitation.
New or Unique Information Provided – This is the first report of the use of IV MMF as adjunctive treatment in dogs with severe generalized myasthenia gravis. Outcome was favorable in all 3 dogs and no adverse effects were noted from the MMF.