040 Necrotising autoimmune polymyositis complicated by rhabdomyolysis and compartment syndrome

Abstract

Background: Necrotising autoimmune myositis (NAM) is a form of idiopathic inflammatory myopathy characterised clinically by acute onset proximal muscle weakness and histologically by myosite necrosis without inflammatory cell infiltration. The underlying aetiologies include drug, autoimmune and metabolic causes and the course of the disease can be severe. We present a case of NAM complicated by respiratory failure, rhabdomyolysis renal failure and compartment syndrome. Methods: A 27 year old male presented with a two week history of acute proximal limb weakness and a non-specific macular rash. Initial laboratory results revealed creatine kinase (CK) 5624IU/L, White cell count 5.0x109/L, C-reactive protein 5mg/L, erythrocyte sedimentation rate 5mm, alanine transaminase 104U/L and creatinine 72umol/L. Extensive viral serology and bacterial cultures were negative. MRI and EMG of lower limbs revealed evidence of myositis. Muscle biopsy showed necrotic myofibres without inflammatory cell infiltrate. Immunohistochemical staining showed sarcolemmal labelling with major histocompatibility class I and deposition of complement on endomysial capillaries suggestive of an autoimmune trigger process. Extensive myositis antibody screens revealed a weakly positive anti-NXP2 and anti-Ku antibodies but negative ANA. Malignancy screen was negative. Despite three pulses of intravenous methylprednisolone, the CK doubled (11,028IU/L). He acutely deteriorated with type 1 respiratory failure and acute kidney injury and was transferred to the intensive care unit (ITU) for ventilatory support and haemofiltration. The CK peaked at 32 000IU/L, however the CRP was only 22mg/L. He subsequently developed compartment syndrome in all four limbs with compartment pressures in the range of 40-50mmHg and required four limb fasciotomies. He was also treated with further methylprednisolone, rituximab and two courses of intravenous immunoglobulin (IVIG). After a short stay on ITU he made a good recovery and was able to mobilise with a walking stick. Upon discharge his CK had normalised and remission was maintained on mycophenolate mofetil and prednisolone. Results: Rhabdomyolysis has been reported in cases of nonnecrotising dermatomyositis. There have also been reports of rhabdomyolysis and compartment syndrome secondary to viral and statin induced myositis. However, to our knowledge we present the first case of NAM complicated by rhabdomyolysis and multiple limb compartment syndrome. This case was also distinctive in requiring fasciotomies and multiple daily lavages for removal of necrotic tissue. Initial treatment with methylprednisolone was ineffective but the patient did respond to rituximab and IVIG treatment. This is consistent with the literature which suggests corticosteroid monotherapy is ineffective for the treatment of NAM with potential efficacy of rituximab and IVIG. Conclusion: This report illustrates a unique case of NAM complicated by rhabdomyolysis and multi-limb compartment syndrome requiring multi-organ support, rituximab, IVIG and fasciotomies. This highlights to the rheumatologist the importance of monitoring for such complications and the potential need for prompt medical, supportive or surgical treatment.