A 19-year-old man with a history of recent-onset asthma presents with chest pain, intermittent claudication and respiratory distress that is unresponsive to bronchodilators and antibiotics. Physical examination reveals mild hypeension (blood pressure = 150/100 mm Hg), bilateral wheezing and numerous purpuric skin lesions on the feet. Laboratory studies demonstrate that leukocytes are increased to 14,000/mL with increased eosinophils and platelets are increased to 450,000/mL. BUN is elevated to 30 mg/dL, and serum creatinine is elevated to 3.5 mg/dL. The serum antineutrophil cytoplasmic antibody test is positive. Urinalysis discloses 3+ proteinuria and RBCs. A renal biopsy demonstrates vasculitis of medium-sized aeries, accompanied by eosinophilia. Which of the following is the most likely diagnosis?

**Core Concept**
The patient's presentation with asthma, vasculitis, and renal involvement suggests an autoimmune-mediated condition. The positive serum antineutrophil cytoplasmic antibody (ANCA) test and renal biopsy findings of medium-sized artery vasculitis with eosinophilia point towards a specific type of vasculitis.

**Why the Correct Answer is Right**
The patient's symptoms and laboratory findings are consistent with eosinophilic granulomatosis with polyangiitis (EGPA), previously known as Churg-Strauss syndrome. EGPA is a type of vasculitis characterized by asthma, eosinophilia, and granulomatous inflammation of small and medium-sized vessels. The presence of ANCA, particularly perinuclear ANCA (p-ANCA), is often seen in EGPA. The renal involvement, as indicated by proteinuria, RBCs, and elevated serum creatinine, is a common complication of EGPA. The eosinophilia and vasculitis of medium-sized arteries on renal biopsy further support this diagnosis.

**Why Each Wrong Option is Incorrect**
**Option A:** Polyarteritis nodosa (PAN) is a type of vasculitis that typically affects medium-sized and small arteries. However, PAN is often associated with hepatitis B infection and typically lacks eosinophilia and asthma. The patient's positive ANCA test and eosinophilia make PAN less likely.
**Option B:** Microscopic polyangiitis (MPA) is a type of vasculitis that affects small vessels and is often associated with MPO-ANCA. MPA typically presents with renal involvement, but the presence of asthma and eosinophilia in this patient makes MPA less likely.
**Option C:** Granulomatosis with polyangiitis (GPA), previously known as Wegener's granulomatosis, is a type of vasculitis that affects small vessels and is often associated with c-ANCA. GPA typically presents with respiratory tract involvement, but the patient's renal biopsy findings of medium-sized artery vasculitis and eosinophilia do not support GPA.
**Option D:** Kawasaki disease is a type of vasculitis that affects medium-sized vessels and is often seen in children. Kawasaki disease typically presents with fever, rash, and lymphadenopathy, but the patient's age, asthma, and eosinophilia make Kawasaki disease less likely.

**Clinical Pearl / High-Yield Fact**
EGPA is a rare autoimmune condition that requires a high index of suspicion. The presence of asthma, eosinophilia, and ANCA positivity, along with renal involvement, should raise suspicion for EGPA.

**Correct Answer:** C. Granulomatosis with polyangiitis (GPA)

✓ Correct Answer: A. Churg-Strauss disease