Diffuse idiopathic myofasciitis in a ferret

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

Olive, an approximately 1-year-old neutered female ferret, presented with mild intermittent diarrhea, weight loss, and lethargy, and her owner noted that she had disappeared several days before arrival. Initial treatment was initiated, including subcutaneous lactated Ringer’s solution (30 mL/kg) for gastrointestinal (GI) symptoms and oral medications for GI distress. Broad-spectrum antibiotics, enrofloxacin (10 mg/kg orally twice daily) and Clavamox Drops (12.5 mg/kg orally twice daily), gastroprotectants in the form of sucralfate (150 mg/kg orally three times daily) and due to lean body status A recovery diet will be offered. He returned 2 days later due to ongoing loss of appetite, diarrhea, and suspected fever. Olive was depressed but responsive with a high fever of 104.3°F, tachycardia (>300 beats/minute), 7% to 10% dehydration, and a palpable abdominal mass in the right cranial abdominal quadrant.

After initial triage and physical examination, complete blood count, chemistry panel and radiographs were performed. Blood test showed mild leukocytosis (8.3 ± 103/mL), high hematocrit (59%), low creatinine (0.1 mg/dL) and serum urea nitrogen (9 mg/dL), and high cholesterol (365 mg/dL). was seen. Whole-body radiographs revealed abnormal contour of the right kidney as well as general dehydration, but serosal details were otherwise normal and there was no evidence of foreign body or obstruction.

Hospitalization and surgery

Due to Olive’s failure to progress in outpatient treatment, hospitalization was implemented to manage dehydration, reduce fever, and treat possible infectious etiologies. Olive had a 24-gauge intravenous (IV) catheter placed in the cephalic vein and was started on IV fluid therapy at 150 mL/kg/day to restore hydration. Since Olive was started on oral medication and had no history of vomiting, previously prescribed oral medications were continued and meloxicam (0.3 mg/kg orally twice daily) was added as an anti-inflammatory. Olive was kept hydrated and hospitalized overnight; at which time his temperature dropped to 103.1°F and his attitude improved marginally to the point where he voluntarily consumed small amounts of high-calorie recovery preserves.

During her continued hospitalization, Olive’s recovery stagnated. Because Olive was not improving and had a palpable mass effect, abdominal exploration surgery was recommended to evaluate the cause of the mass and remove it if necessary. Her owners approved this plan, and 48 hours after being admitted to the hospital, Olive underwent surgery. He was placed in the standard supine position and covered with a quarter drape. The abdomen was opened via a standard midline approach, revealing the right kidney to be extensively covered by fluid-filled cysts with loss of normal architecture. No other abnormalities were noted, and the right kidney was removed without complications, and hemostasis was achieved by placing a hemoclip along the renal artery, vein, and ureter. After sterile abdominal lavage, the body wall and skin were closed in 3 layers using monofilament absorbable sutures. The kidney was sent for histopathology and a sterile swab sample of several ruptured cysts was sent for culture. Olive was discharged from the hospital 24 hours after surgery; he was more active, ate better, and had a normal body temperature (101°F).

Histopathology results

Histopathology and culture of the kidney were returned; multifocal renal cysts, moderate chronic pyelonephritis with hydronephrosis, and pyogranulomatous peritonitis without evidence of bacteria or other infectious neoplastic agents were seen. After 96 hours, the kidney culture came back with no growth, and although Olive had been on antibiotics for 24 hours before surgery, this was thought unlikely to cause a false-negative culture given the number of cysts and the amount of inflammation present. Based on 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 disease.

To follow

Olive returned 1 week after nephrectomy with worsening condition with 7% to 10% dehydration, fever (104°F), anorexia, and severe lethargy. By this visit, our differential list had been narrowed to include sepsis and disseminated idiopathic myofasciitis (DIM). Blood work was repeated and Olive showed several changes thought to be due to 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 in blood work indicating that the primary disease process is DIM include a severe neutrophilia with toxic changes (18,998/mL), a severe leukocytosis (32.2 x 103/mL) characterized by severe lymphocytosis (11,914/mL), a moderate degree of thrombocytosis (680 x103/mL), low total protein (4.8 g/dL), low albumin (1.8 g/dL), and slightly elevated chloride (114 mEq/L).

Due to lack of response to treatment and increased suspicion of DIM, the decision was made to change Olive’s antibiotics and start immunosuppressant steroids in an attempt to improve her clinical symptoms: enrofloxacin was stopped and replaced with doxycycline (10 mg/kg orally twice). famotidine (0.5 mg/kg orally twice daily) and prednisolone (0.5 mg/kg orally twice daily). Over the next few days, Olive showed no improvement despite changes in her treatment plan and her quality of life continued to decline. Therefore, the owners chose humane euthanasia.

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

The prognosis for this condition is poor and its etiology remains unknown but is suspected to be autoimmune. There have been some cases where systemic immunosuppression using steroids and other immunosuppressants has caused remission. Olive’s histopathology combined with her history is the most obvious indicator of DIM and her postmortem diagnosis.