Congenital and acquired neuromuscular disease of young dogs and cats

Neuromuscular disorders in small animals include a diverse group of congenital and acquired diseases. The prognosis will vary according to the disorder and the portion of the motor unit affected. A number of diseases might be satisfactorily treated (for example, myasthenia gravis, congenital myotonia), whereas others may be self-limiting (for example, hereditary myopathy of Labrador Retrievers). Accurate diagnosis is necessary for establishing a prognosis and treatment plan suitable to the patient and client. Specific diagnosis in the absence of specialized tests is difficult, although not always impossible (for example, congenital myotonia in the Chow Chow). A knowledge of the neuromuscular diseases that might affect small animals, a detailed history, and a thorough physical examination will help in the presumptive diagnosis. Specialized laboratory examinations may need to be applied (for example, antiacetylcholine receptor antibody titer for acquired myasthenia gravis). Referral may be necessary for more detailed diagnostic workup (for example, electromyographic examination, nerve or muscle biopsy examination). In the case of inherited neuromuscular disorders, a knowledge of inheritance patterns will allow genetic counseling to avoid future problem breedings.     

Congenital retrosternal (Morgagni) diaphragmatic hernias in three horses

CASE DESCRIPTION: 3 Horses were examined and treated because of sudden onset of signs of abdominal pain. CLINICAL FINDINGS: All horses had a retrosternal (Morgagni) hernia involving the right side of the diaphragm. In each horse, the large colon was incarcerated in a right muscular defect in the diaphragm with a large hernial sac. TREATMENT AND OUTCOME: Definitive surgical repair of the hernia was not performed during the initial celiotomy. The hernia was repaired with mesh herniorrhaphy, but without resection of the hernia sac in 2 horses. For 1 horse, conservative management was applied. In the 2 horses treated with surgical correction, no major postoperative complications developed, and all 3 horses have been free of signs of abdominal pain. CLINICAL RELEVANCE: Horses with retrosternal hernias involving the diaphragm can develop clinical signs of intermittent obstruction of the large colon and chronic colic. In horses, retrosternal diaphragmatic hernias appear to develop exclusively in the right ventral aspect of the diaphragm and could represent an embryologic defect of diaphragm formation. Affected horses can be successfully treated with mesh herniorrhaphy or, in some instances, with conservative management.     

Metastatic melanomas in young broiler chickens (Gallus gallus domesticus)

Four young broiler chickens affected by multiple melanotic tumors are described. Grossly, there were multiple tumors composed of melanocytes within the skin, skeletal muscle, and multiple visceral organs. Tumors ranged from flattened macules to masses that extensively replaced viscera. Microscopically, melanocytes were often well pigmented, and while there was moderate nuclear anisokaryosis, mitotic rates were low. Immunohistochemical staining of some melanomas with antibodies to S100 proteins, Melan-A, vimentin, or neuron-specific enolase after bleaching of tumor cells with potassium permanganate revealed lack of immunostaining of tumor cells with antibodies to S100, strong positive staining of tumor cells for neuron-specific enolase, moderate staining with antibodies to vimentin, and faint staining for Melan-A. Only neuron-specific enolase staining was evident in unbleached tumor cells. Attempts to identify exogenous avian leukosis viruses in these tumors were unsuccessful.     

Cimetidine for treatment of melanomas in three horses

Cimetidine, an H2 histamine antagonist, was used in the clinical management of progressive, multifocal melanomatosis in 3 adult gray horses. Prior to treatment, the tumors had increased rapidly in size and number in 2 horses (duration of 6 and 27 months, respectively) and slowly in the third horse (duration of 48 months). All 3 horses were treated with cimetidine (2.5 mg/kg of body weight, PO, q 8 h) for 2 months to 1 year. During treatment, the number and size of the melanomas decreased substantially (50 to 90%). The progression of the disease was halted in 2 horses and controlled in the third horse, which is still being treated with cimetidine (1.6 mg/kg, PO, q 24 h). The horses in which treatment was terminated have not been treated for 31 and 41 months, respectively, during which time the melanomas have not increased in number or size.     

Dental benign cementomas in three horses

Cementoma is a very rare odontogenic neoplasm of mesenchymal origin. Clinically, in 3 horses, multiple bony enlargements of the upper and lower jaw extending into the oral cavity were observed. Radiographically, multiple, well-circumscribed, radiopaque masses surrounding the roots of the upper and lower incisors or an upper premolar tooth were present. Due to malocclusion and local pain, single teeth were extracted in each case. Grossly, a hard grayish-white mass surrounding the root of the incisors and the premolars was identified. Histopathologically, the tumors consisted of excessive deposition of cementum-like tissue. Cells, resembling cementoblasts, lined irregularly shaped lacunae, which were present in the tumor tissue, and showed minimal cellular pleomorphism. Mitotic figures were not present. Macroscopically and histologically, all 3 equine cases displayed great similarities to cementomas in other species. However, due to their high degree of differentiation, hypercementosis must be considered as a differential diagnosis.     

Hemangiosarcoma in 11 young horses

Hemangiosarcoma is a rare neoplasm of horses and hemangiosarcoma in young horses might behave differently than in mature horses. The purpose of this study was to identify the characteristics of hemangiosarcoma occurring in horses < or = 3 years of age. Medical records from 1982 to 2004 were searched for horses < or = 3 years of age with a histopathologic diagnosis of hemangiosarcoma. Eleven records were identified. Thoroughbred and Thoroughbred crosses predominated. Age ranged from 9 days to 3 years. All horses presented with cutaneous or leg swellings or joint effusion. Physical examination findings included tachycardia, fever, and depression. Laboratory abnormalities included anemia (5/11), hyperfibrinogenemia (4/11), hypofibrinogenemia (3/11), thrombocytopenia (2/11), and neutrophilic leukocytosis (1/11). Ultrasonographic and radiographic evaluation was not diagnostic in any case. Antemortem histopathologic diagnosis was obtained in 10 cases. Six of 11 horses were euthanized. Surgical resection was performed in 5 horses, 2 of which were later euthanized. Diagnosis was confirmed histologically at postmortem examination in all euthanized horses. Two cases resolved spontaneously. Early histopathologic diagnosis may allow cure if the mass is localized and amenable to surgical resection. In cases where the horse is medically stable, and masses are not interfering with quality of life, a period of observation may be warranted.     

Congenital dilatation of the bile ducts (Caroli's disease) in young dogs

We describe 8 young dogs with congenital dilatation of the intra- and extrahepatic bile ducts and diffuse cystic kidney disease, compatible with Caroli's disease in humans. The dogs were referred between 1980 and 2000 because of chronic disease at an age of 6 months to 3 years. These dogs included 3 Collies, 2 Frisian Stabyhouns, 2 Jack Russell Terriers, and 1 mixed-breed dog. The most common signs were vomiting (6/6), polyuria and polydipsia (4/6), and anorexia (4/6). Ascites was a common finding (4/6). Clinicopathologic abnormalities were available for 6 dogs. All had increased plasma alkaline phosphatase activity and fasting bile acids: increased alanine aminotransferase activity and urea and creatinine concentrations were present in 50% of dogs. Ultrasound examination of the liver showed severely dilated bile ducts without evidence of obstruction, and calcification in all cases but 1. Postmortem examination revealed severe dilatation of the larger intra- and extrahepatic bile ducts. The common bile duct and gall bladder were normal, and the bile system was patent. The ducts contained a clear viscid fluid often with calcified material. Microscopically, marked portal fibrosis was present, often with abnormally structured dilated bile ducts lined with columnar or cuboid epithelium and regularly small calcifications. The lesion was complicated by ascending cholangitis in 1 dog. The kidneys showed marked cortical and medullary fibrosis with a diffuse radial cystic pattern; only slight renal fibrosis was found in the oldest dog. Seven dogs were euthanized without treatment; the oldest dog was alive and well 5 months after diagnosis and was maintained on a protein-restricted diet.     

Temporohyoid osteoarthropathy in two young horses

Two cases of temporohyoid osteoarthropathy (THO) in young Australian horses are described. The pathogenesis of THO is yet to be fully elucidated, but current theories include extension of infection from otitis media or interna to the temporohyoid joint or a primary but non‐infectious degenerative condition within the temporohyoid joint. The young age of the horses and the unilateral distribution suggested an infectious aetiology. Both horses partially responded to treatment with broad‐spectrum antimicrobial and anti‐inflammatory drugs with concurrent management of ulcerative keratitis. The management of violent head shaking in one horse included the administration of gabapentin, an anticonvulsant known to have antihyperalgesic effects and reduce neuropathic pain.     

Nasomaxillary fibrosarcomas in three young horses

Nasomaxillary fibrosarcoma was diagnosed in 3 young horses. Clinical signs included epiphora, facial swelling, dyspnea, unilateral serosanguineous nasal discharge, or an external mass. Physical examination, radiography, and cytology were important diagnostic adjuncts. The definitive diagnosis in each case was based on biopsy. In one case, surgical removal of the tumor and extensive curettage of the affected sinus resulted in extended remission from neoplastic disease.     

Maxillary odontogenic myxoma in young horses: Six cases (2003–2011)

Six young horses presented with a rapidly expanding maxillary mass with concurrent nasal discharge. All horses had a nonpainful firm unilateral facial swelling centred over the maxillary sinuses, accompanied by mucopurulent nasal discharge. Diagnostic imaging revealed an infiltrative nasomaxillary mass with cheek tooth involvement, diagnosed as odontogenic myxoma. The tooth involvement included missing, malformed and/or displaced dental precursors or unerupted teeth. Due to the rapid expansion and extent of the masses, and the poor prognosis reported for surgical excision, euthanasia was recommended and performed in all cases. Macroscopically, a soft oedematous tissue with a grey to green colour was seen in the regions of missing, malformed or displaced dental precursors or unerupted teeth. Histologically, this tissue consisted of spindle shaped cells surrounded by an abundant homogenous pale stroma, rich in acid mucopolysaccharides. Immunohistochemistry was positive for actin and the mesenchymal marker vimentin. The cheek tooth involvement identified in the described cases resembled what is previously reported in odontogenic myxoma in children and young adults. Even in man, maxillary odontogenic myxoma represents a therapeutic challenge due to the invasiveness of the lesions and radical surgical excision is recommended. Treatment is further complicated by sinonasal involvement. Surgery was not attempted in the cases presented here due to the extent of the lesions and the risk of recurrence. Clinicians should be aware of this rare condition when presented with young horses with sinonasal neoplasia.     

Plasma concentrations of endothelin-like immunoreactivity in healthy horses and horses with naturally acquired gastrointestinal tract disorders

OBJECTIVE: To compare plasma endothelin (ET)- like immunoreactivity between healthy horses and those with naturally acquired gastrointestinal tract disorders. ANIMALS: 29 healthy horses and 142 horses with gastrointestinal tract disorders. PROCEDURE: Blood samples were collected from healthy horses and from horses with gastrointestinal tract disorders prior to treatment. Magnitude and duration of abnormal clinical signs were recorded, and clinical variables were assessed via thorough physical examinations. Plasma concentrations of ET-like immunoreactivity were measured by use of a radioimmunoassay for human endothelin-1, and CBC and plasma biochemical analyses were performed. RESULTS: Plasma ET-like immunoreactivity concentration was significantly increased in horses with gastrointestinal tract disorders, compared with healthy horses. Median plasma concentration of ET-like immunoreactivity was 1.80 pg/ml (range, 1.09 to 3.2 pg/ml) in healthy horses. Plasma ET-like immunoreactivity was greatest in horses with strangulating large-intestinal obstruction (median, 10.02 pg/ml; range, 3.8 to 22.62 pg/ml), peritonitis (9.19 pg/ml; 789 to 25.83 pg/ml), and enterocolitis (8.89 pg/mI; 6.30 to 18.36 pg/ml). Concentration of ET-like immunoreactivity was significantly associated with survival, PCV, and duration of signs of pain. However, correlations for associations with PCV and duration of pain were low. CONCLUSIONS AND CLINICAL RELEVANCE: Horses with gastrointestinal tract disorders have increased plasma concentrations of ET-like immunoreactivity, compared with healthy horses. The greatest values were detected in horses with large-intestinal strangulating obstructions, peritonitis, and enterocolitis. This suggests a potential involvement of ET in the pathogenesis of certain gastrointestinal tract disorders in horses.