A18‐year‐old healthy female presented to her primary care physician in early April with isolated right calf pain. Her initial workup included an ANA, D‐dimer, Epsteinn‐Barr virus, erythrocyte sedimentation rate (ESR), creatine kinase, and creatinine, all of which were within normal limits. An MRI of the brain and spines and ultrasound of lower extremities were also negative. In the subsequent 2 months, the myalgia spread to all extremities and became so severe she was unable to attend high school and was wheelchair bound. In late May, she presented to the emergency room for severe polyarthralgia and myalgia and was found to have an elevated creatinine of 1.53 mg/dL compared with 0.56 mg/dL 2 months prior. In June, she was referred to the Department of Nephrology for evaluation of acute renal failure. During this visit, she reported a 15‐pound weight loss, night sweats, chills, joints swelling, and reddish skin changes on her arms and lower extremities. Physical examination was significant for diffuse tender arms, reddish livedo reticularis on right arm and right foot, and a right foot drop. Further workup included ESR 102 mm/h, C‐reactive protein 11.3 mg/dL, hemoglobin 10 g/dL (compared with 12.8 g/dL in April), antimye‐loperoxidase (MPO‐ANCA) positive at 1.1 (0–0.9), and ANA 1:160 speckled. Urine revealed red blood cell casts, and a urine protein/creatinine ratio of 2.3 mg/mg. A percutaneous renal biopsy was interpreted as pauci‐immune crescentic glomerulonephritis (PICGN). She was immediately started on high‐dose methylprednisolone 1 g daily for a total of 3 doses, followed by 60 mg prednisone and intravenous 0.75 g/m2 cyclophosphamide. Within 1 month her rash, myalgia, and arthralgia had disappeared. She had regained her lost weight, and her creatinine returned to its baseline value.
Microscopic polyangiitis (MPA) is a rare disease in the young adult. The median age of onset of ANCA‐associated vasculitis ranges from 50s to 62 years old. MPA is characterized by angiitis of small‐sized vessels, and renal involvement is typically rapidly progressive, leading to renal failure and dialysis. Because of diverse organ involvement and multisystem symptoms, diagnosis can be elusive. Myalgia has been described as a symptom of polyarteritis nodosa but not as a presenting manifestation of MPA. Microscopic polyangiitis (MPA) is associated with significant morbidity and often rapidly developing organ involvement, especially the kidneys and peripheral nerves. Therefore, an early diagnosis is of considerable importance, both for early initiation of aggressive immunosuppressive treatment and for preservation of organ function. Because of this patient's young age and atypical presenting features of severe myalgia, the diagnosis was difficult.
When a patent of any age presents with significant arthralgia and myalgia, a careful history, physical examination, and urinalysis are important to rule out the unusual possibility of a systemic necrotizing vasculitis.
K. Tamura ‐ none; S. Shoor ‐ none