Disseminated idiopathic myofasciitis in ferrets (myositis, polymyositis) is a severe suppurative inflammatory myopathy of young pet ferrets affecting skeletal muscle and surrounding connective tissue. It presents acutely with weakness, depression, fever, anorexia, dehydration, and rapid deterioration.

Pathophysiology

Inflammation of skeletal muscle leads to weakness, myalgia, and atrophy. The cause is unknown and thought to be autoimmune or immune-mediated.

Systems affected

  • neuromuscular: inflammation in muscle and connective tissue;
  • GI: diarrhoea sometimes;
  • lymphatic: lymph node enlargement;
  • respiratory: nasal discharge or dyspnoea;
  • cardiovascular: myocardial involvement.

All ferrets may be affected; most cases are under 18 months. No sex predisposition.

Onset is acute or subacute with rapid worsening (often within 12–36 hours). Recent vaccination may be noted.

Physical examination

Affected ferrets may show (roughly in order of frequency):

  • fever (40–42 °C);
  • lethargy;
  • paresis;
  • depression;
  • anorexia;
  • dehydration;
  • pain in tail base area (pelvic limbs and lumbosacral region, hyperesthesia);
  • abnormal faeces;
  • lymphadenopathy;
  • weight loss;
  • tachycardia/murmur;
  • serous nasal discharge;
  • ocular discharge;
  • cough;
  • oedema;
  • seizures.

Definitive diagnosis is by histopathology of affected skeletal muscle.

Differential diagnoses

  • neoplasia;
  • Aleutian disease;
  • coronavirus;
  • sarcocystosis;
  • toxoplasmosis;
  • myasthenia gravis;
  • trauma;
  • bacterial infection.

Diagnosis

Bloodwork may show moderate or marked mature neutrophilia (left shift) with mild or moderate toxic neutrophil changes, mild to moderate normocytic anaemia (often non-regenerative), mild hyperglycaemia and hypoalbuminaemia, mild ALT elevation.

Imaging may show splenomegaly and enlarged mesenteric lymph nodes.

Treatment

Hospitalisation for supportive care is required; prognosis is usually poor and treatment may be prolonged.

Medications used:

  • prednisolone (1 mg/kg);
  • cyclophosphamide (10 mg/kg);
  • chloramphenicol (50 mg/kg).

Prognosis is guarded to poor.

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