P152 A rare case of necrotising vasculitis presenting with calf swelling in a 15-year-old female

Abstract

Abstract Background/Aims We present the case of MF, a 15-year-old female who presented to the paediatric clinic with swelling and pain affecting her right calf. She was previously fit and well. Initial imaging was suggestive of localised myositis but a subsequent muscle biopsy was in keeping with necrotising vasculitis. Methods In May 2021, MF presented to a general paediatric clinic with a 6-week history of right lateral calf pain and swelling to the lateral border of the right proximal fibula. She was systemically well. Blood tests and an x-ray were normal. An ultrasound scan of the right calf showed fusiform thickening of the peroneus longus muscle proximally. There was no discrete mass. The appearance was thought to be an inflammatory process such as myositis. An MRI scan was advised. Over the course of the next few weeks, the swelling and pain to the right calf progressed and she was unable to fully weight bear. Repeat blood tests were normal except CRP 11. CK was normal. At the end of June, an MRI scan of the right lower leg showed significant swelling and oedema along the length of the peroneus longus musculature as demonstrated on ultrasound. Florid oedema extended to involve the soleus and to a lesser extent the lateral head of gastrocnemius. There was thickening and oedema through the subcutaneous fat circumferentially compared to the left side (see images). The appearances were thought to be consistent with myositis but an inflammatory malignancy could not be fully excluded and an opinion from the Birmingham team was recommended. The Birmingham MDT advised that malignancy was unlikely but a CT scan was recommended. The CT scan confirmed the MRI findings (see image). Results MF's symptoms progressed rapidly over a short period of time with diffuse swelling of the right lower limb with associated pain and numbness. She also developed purpuric lesions around the ankle (see photos). The CRP increased to 59 and then 123. CK remained normal. Local rheumatology opinion was sought once malignancy had been excluded. The initial impression was of a focal myositis but a muscle biopsy was requested urgently. IV steroids were administered followed by high dose oral prednisolone as a reducing course. The symptoms improved rapidly. The subsequent biopsy showed a florid necrotising vasculitis affecting the small-medium arterial vessels. There was no evidence of myositis (see image). ANCA was negative and CT renal and abdominal angiogram was normal. Nerve conduction studies showed a very severe sensory lesion of the right sural nerve, which explained the persistent numbness. Mycophenolate mofetil was added and clinical improvement is ongoing. Conclusion We present a rare case of localised vasculitis in the right calf. A literature review indicates this is the first case presented in an adolescent. Disclosure S.C. Earl: None. J. Smith: None. A. Ramanan: Grants/research support; Abbvie.