Disseminated idiopathic myofasciitis in a ferret

Olive at CityVet (Images courtesy of Cordell Rech, DVM60)

Olive, an approximately 1-year-old spayed female ferret presented with mild intermittent diarrhea, decreased weight, and lethargy, and her owner noted she had gone missing for several days prior to arrival. Initial treatment for her gastrointestinal (GI) symptoms was started, including subcutaneous lactated Ringer’s solution (30 mL/kg) and oral medications for GI upset. Broad-spectrum antibiotics consisted of enrofloxacin (10 mg/kg orally twice a day) and Clavamox Drops (12.5 mg/kg orally twice a day), gastroprotectants in the form of sucralfate (150 mg/kg orally 3 times a day), and a recovery diet to be offered due to lean body condition. She returned 2 days later for continued inappetence, diarrhea, and suspected fever. Olive was depressed but responsive, with an elevated temperature of 104.3 °F, tachycardia (>300 bpm), 7% to 10% dehydration, and a palpable abdominal mass in the right cranial abdominal quadrant.

After initial triage and physical examination, a complete blood count, chemistry panel, and radiographs were performed. Blood work showed mild leukocytosis (8.3 103/mL), elevated hematocrit (59%), low creatinine (0.1 mg/dL) and serum urea nitrogen (9 mg/dL), and elevated cholesterol (365 mg/dL). Full-body radiographs revealed abnormal contour to the right kidney as well as generalized dehydration but otherwise normal serosal detail and no evidence of a foreign body or obstruction.

Hospitalization and surgery

Due to Olive’s lack of improvement on outpatient therapy, hospitalization was implemented to manage dehydration, reduce pyrexia, and treat for possible infectious etiologies. Olive had a 24-gauge intravenous (IV) catheter placed in a cephalic vein and was started on IV fluids at a rate of 150 mL/kg/day to restore hydration. Since Olive was already started on oral medications and there was no history of emesis, the oral medications previously prescribed were continued and meloxicam (0.3 mg/kg orally twice a day) was added as an anti-inflammatory. Olive was maintained on overnight fluids and hospitalization, during which her fever dropped to 103.1 °F and her attitude improved marginally to the point where she voluntarily consumed small amounts of a high-calorie recovery canned food.

During continued hospitalization, Olive’s improvement plateaued. Since Olive was not improving and there was a palpable mass effect, abdominal exploratory surgery was recommended to assess the cause of the mass and remove if indicated. The owners approved this plan, and 48 hours after hospitalization, Olive was taken to surgery. She was placed in standard dorsal recumbency and quarter-draped. The abdomen was opened in a standard midline approach, which revealed the right kidney to be diffusely covered in fluid-filled cysts with loss of normal architecture. No other abnormalities were seen, and the right kidney was removed without complication and hemostasis was managed by hemoclip placement across the renal artery, vein, and ureter. After sterile lavage of the abdomen, the body wall and skin were closed in 3 layers using a monofilament absorbable suture. The kidney was submitted for histopathology, and a sterile swab of several ruptured cysts was sent in for culture. Olive was discharged from the hospital 24 hours postoperatively, being more active, eating well, and with a normal temperature (101 °F).

Histopathology results

Histopathology and culture for the kidney returned, showing multifocal renal cysts, moderate chronic pyelonephritis with hydronephrosis, and pyogranulomatous peritonitis without evidence of bacteria or other infectious neoplastic agents. After 96 hours the renal culture returned with no growth, and although Olive had been on antibiotics for 24 hours prior to surgery, this was considered unlikely to cause a false negative culture given the number of cysts and amount of inflammation present. Due to the clinical history and diagnostic findings, it was concluded that Olive’s abnormal kidney was an incidental finding and not a primary factor in her illness.

Follow-up

Olive returned 1 week post nephrectomy due to worsening condition with 7% to 10% dehydration, returned pyrexia (104 °F), anorexia, and severe lethargy. At this visit, our differential list had been narrowed to include sepsis and disseminated idiopathic myofasciitis (DIM). Blood work was repeated, and Olive had several changes considered to be caused by the recent nephrectomy: low hematocrit (32%), low red blood cell count (6.3 x 106/mL), and low hemoglobin (9.6 g/dL). Clinically significant changes to her blood work that gave indication to the primary disease process being DIM were a severe leukocytosis (32.2 x 103/mL) characterized by a severe neutrophilia with toxic changes (18,998/mL), severe lymphocytosis (11,914/mL), moderate thrombocytosis (680 x103/mL), low total protein (4.8 g/dL), low albumin (1.8 g/dL), and mildly elevated chloride (114 mEq/L).

Due to the lack of response to treatment and the increasing suspicion of DIM, the decision was made to switch Olive’s antibiotics and begin immunosuppressive steroids in an effort to improve her clinical signs: enrofloxacin was stopped and replaced with doxycycline (10 mg/kg orally twice a day), famotidine (0.5 mg/kg orally twice a day), and prednisolone (0.5 mg/kg orally twice a day). Over the next several days, Olive showed no improvement despite the changes to her treatment plan and quality of life continued to decline. Due to this, her owners elected humane euthanasia.

After euthanasia, muscle biopsies were taken from the diaphragm, esophagus, and gastrocnemius muscles for histopathology. Histopathology showed severe suppurative esophagitis and myositis with pyogranulomas. DIM typically affects young ferrets under 18 months of age and is not contagious, and onset is typically fast; owners may report overnight changes to attitude and behavior as well as persistent but fluctuating fever. Initial blood work may show normal to mildly elevated white blood cell counts, as in Olive’s case, which can rapidly progress over 7 to 10 days up to 100,000 cells/mL of blood with toxic changes. Glucose is frequently elevated and albumin levels are usually decreased, while creatine kinase is not elevated. Biopsy of affected muscle typically reveals severe, widespread inflammation often with suppurative changes, with the esophagus being particularly affected.

Prognosis for this condition is poor, and the etiology is still unknown but suspected to be autoimmune. There have been some cases where systemic immunosuppression has caused remission using steroids and other immunosuppressants. Olive’s histopathology combined with her history is most indicative of DIM and was her postmortem diagnosis.