Case Presentation: An 85-year-old male presented to his cardiologist for right leg swelling and redness. Lower extremity ultrasound was negative for a DVT, and cephalexin was prescribed for suspected cellulitis. Over the next five days, the patient’s symptoms worsened and he was admitted twice to the hospital for intravenous antibiotics. After the patient was discharged on oral antibiotics, he noticed frothy-appearing urine with frank hematuria. He presented to his primary care physician’s office, where his creatinine was found to be 4.5 mg/dL, up from baseline of 1 mg/dL. His albumin was 2.3, total protein 4 g/dL and his liver function tests were normal. Urinalysis showed 1+ proteinuria and 76 red blood cells per high-power field. Physical examination was significant for pitting edema and erythematous patches with overlying palpable purpura on the bilateral lower extremities. Further laboratory testing revealed a titer of p-ANCA of 1:320. Skin biopsy revealed pathology consistent with microscopic polyangiitis. Due to worsening renal function, a kidney biopsy was done and showed pauci-immune type III necrotizing and crescentic glomerulonephritis, confirming the diagnosis of microscopic polyangiitis with ANCA-associated glomerulonephritis. The patient was treated with rituximab and methylprednisolone followed by a prednisone taper, with reduction of Cr to 2.9 mg/dL four weeks later and then to 2.1 mg/dL after 6 weeks He continued to be followed by nephrology as an outpatient.
Discussion: This patient presented with microscopic polyangiitis causing rapidly progressive glomerulonephritis and acute renal failure. Microscopic polyangiitis is a systemic small vessel vasculitis that results in renal impairment in majority of patients if early diagnosis and treatment are delayed. The treatment regimen normally consists of corticosteroids with or without immunosuppressive drugs, and in cases of severe disease, plasmapheresis to remove the main culprit, ANCA, from the blood.
Conclusions: This case illustrates the nonspecific presentation of ANCA-associated vasculitis through its resultant ability to mimic cellulitis. Additionally, this case stresses the importance of a thorough history, complete physical examination, and broad differential diagnosis. This is imperative for preventing misdiagnosis, avoiding any further unnecessary diagnostic tests or treatments, and initiating appropriate therapy in a timely manner.
