CASE REPORTSE05. PROXIMAL MYOSITIS DEVELOPING AFTER PROSTATIC RADIOTHERAPY

Abstract

Background: Myositis is an inflammatory condition often associated with autoimmune conditions or as a side effect of medications such as statins. It can cause pain and weakness which may result in significant disability. We report a case of myositis occuring after radiotherapy for treatment of prostatic cancer. Myositis causing pain and weakness in the absence of other neurological symptoms is a rare complication of radiotherapy treatment, most commonly reported in the context of lymphoma treatment. The first reported case of radiotherapy induced proximal myositis of the hip flexors has recently been described in a patient receiving radiotherapy for locally invasive bowel cancer but to the best of our knowledge this is the first reported case occurring after prostatic radiotherapy. Methods: A 75 year old man with a history of gout and prostate carcinoma presented with a four day history of new onset acute progressive leg weakness and significant bilateral thigh pain. He reported that the pain and weakness began two days after the start of an acute flare of gout affecting the MTP joints for which he was taking NSAIDs. He was found to have 3/5 power of knee extensors bilaterally with 5/5 power of all other lower limb muscles and no other neurology. Results: CRP, ESR and WCC were raised at 243 mg/L, 84 mm/hr and 12.4 ×109 cells/L respectively, while CK was normal at 300 IU/L. Myositis, vasculitis and viral screens were all negative. EMG and Nerve Conductions Studies were unremarkable. MRI of the thigh demonstrated symmetrical diffuse oedema of the hip adductors, tensor fascia latae and obturator externi consistent with proximal myositis. On admission he was started on colchicine for his gout and within two days the pain and weakness began to resolve. Three days post admission his symptoms had completely resolved, he was able to fully mobilize and there was 5/5 power of all lower limb muscles. Given the unusual symmetrical nature of the myositis, the normality of all investigations except the MRI and the spontaneous resolution of symptoms, the myositis was likely caused by his final prostatic radiotherapy session occurring two weeks prior to symptom development. Conclusion: The present case demonstrates that radiotherapy induced myositis is an important differential for patients presenting with a proximal lower limb myositis and a past history of radiotherapy for prostate cancer. Further the similarity in presentation to the recently reported case of proximal myositis developing shortly after radiotherapy for bowel carcinoma suggests that this may be a more common complication of radiotherapy than previously appreciated.