Focal myasthenia gravis as a paraneoplastic syndrome of canine thymoma: improvement following thymectomy

Abstract

A 10-year-old, neutered male cocker spaniel-cross experienced regurgitation, dry retching, and weight loss. A large, mediastinal mass and dilatation of the esophagus were seen on thoracic radiographs. Cytological, histopathological, immunohistochemical, and serological findings were consistent with a lymphoepithelial thymoma and focal, esophageal myasthenia gravis. Surgical removal of the mass resulted in rapid resolution of the megaesophagus and a decrease in serum acetylcholine-receptor antibody concentration. The dog was clinically normal until the thymoma recurred six months postoperatively. Clinical signs, diagnostic evaluation, management, and treatment of a dog with thymoma and megaesophagus are described.

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

“…In both the human and veterinary literature, there are conflicting reports of continued clinical signs of MG versus remission of clinical signs after surgical removal of thymoma 7, 11, 12, 25, 26, 27, 28, 29, 30, 31, 32, 33. Studies in myasthenic people include both cases of thymic hyperplasia and thymoma.…”

Thymoma related myasthenia gravis in humans and potential animal models

“…The latter is not only indicated for oncologic reasons [136] but can reduce autoantibody titers and myasthenic symptoms [128].…”

“…TAMG in dogs and cats typically starts at a sudden with generalized symptoms that largely resemble those in humans, including muscle weakness and fatigability, dyspnea and tachypnea, dysphagia, [104,127]. Due to a key role of skeletal muscle in esophageal function in dogs, megaesophagus is a typical presenting symptom in myasthenic dogs that may occur as focal sign and generally heralds a poor prognosis due to aspiration pneumonia [121,128]. As a possible hint to a similar pathogenesis of canine,…”

“…In both canine and feline TAMG, myasthenic symptoms are typically elicited by AChRautoantibodies [108,128,129], but a rare cases with (questionable) "sero-negative" canine TAMG has been described [130]. Furthermore, anti-striational (anti-titin and anti-ryanodine receptor) antibodies appear to show a similar association with thymoma, TAMG and nonthymomatous MG at old age in dogs and humans [131,132], while the correlation is unknown or less clear in thymoma-bearing rodents [125].…”

Perioperative Mortality and Long‐Term Survival in 80 Dogs and 32 Cats Undergoing Excision of Thymic Epithelial Tumors

“…[9][10][11][12] Clinical signs may also result from paraneoplastic syndromes including myasthenia gravis 11,[13][14][15][16][17][18][19][20][21][22][23] or polymyositis in dogs and cats, 19,24 hypercalcemia in dogs, 11,13,25,26 and exfoliative dermatitis in cats. 24,[27][28][29][30][31] Concurrent non-thymic cancers 11,18 and T-cell lymphocytosis 32 have also been reported in dogs.…”