Immune-mediated necrotising myopathy: a rare cause of hyperCKaemia

Progressive increases in creatine kinase activity in an anorexic cat with necrotising myopathy

Case summary

A 5-year-old castrated male domestic shorthair cat with weight loss and reduced appetite was evaluated for increased and progressively rising creatine kinase (CK) activity. The cat had recently been diagnosed with hepatic lipidosis. Muscle biopsy and histopathology revealed mild myonecrosis and phagocytosis without obvious inflammatory cell infiltrates. Resolution of necrotising myopathy was observed after a short course of anti-inflammatory prednisolone and nutritional supplementation.

Relevance and novel information

This is the first report of a necrotising myopathy in a cat associated with progressively increasing CK activity and decreased appetite. Anorexia in cats has been associated with increased CK activity, but an underlying cause of this CK elevation has only been postulated. Here we document muscle necrosis and muscle stiffness in a cat with anorexia.

Immune-Mediated Necrotizing Myopathy Initially Presenting as Erythema Nodosum

Immune-mediated necrotizing myopathy (IMNM) is a type of autoimmune myopathy characterized by severe diffuse proximal myofiber necrosis in the context of inflammatory myopathy. Autoantibodies of anti-signal recognition particle and anti-hydroxy-3-methylglutaryl-CoA reductase are two antibodies specific to IMNM. Erythema nodosum (EN) is often accompanied by various systemic diseases, such as autoimmune diseases. Herein, we report a female patient with signal recognition particle-associated IMNM, with EN as the first presentation. She showed significant clinical improvement after the initiation of glucocorticoids, intravenous immunoglobulin, rituximab, and mycophenolate mofetil. This case indicates that IMNM can initially present as EN. IMNM and EN might have overlapping pathogeneses.

Anti-HMGCR myopathy presenting with acute systolic heart failure

Necrotising autoimmune myopathy (NAM) is an immune-mediated myopathy that may be associated with statin use, malignancy or an autoimmune connective tissue disease, but it can also be idiopathic. Anti-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) myopathy is an extremely rare side effect of statin use, occurring in approximately 2-3 out of every 100 000 patients who use statins. Patients typically present with subacute proximal muscle weakness and creatine kinase levels >10 times the upper limit of normal. The diagnosis is suggested by muscle biopsy showing necrotic fibres with minimal inflammation along with positive anti-HMGCR antibodies. Treatment nearly always requires multiple immunosuppressive agents, the earlier use of which is associated with improved outcomes. Reports of statin-induced NAM leading to heart failure are limited. We present the case of a 69-year-old woman with statin-induced NAM who presented with acute systolic heart failure. Early initiation of high-dose corticosteroids and IVIG resulted in significant improvement in her symptoms.