A 24 year old man presents with a non-productive cough and worsening exertional dyspnea for 1 month, associated with intermittent chills and night sweats. He was treated with Roxithromycin + Amoxicillin for 2 weeks, with no response. His basic investigations are significant for an Hb of 6.0 g/dL with normal leukocyte and platelet counts, and a serum creatinine of 1.6 mg/dL, with an eGFR of 30 ml/min/1.73m2. A CXR shows pulmonary infiltrates in the lower regions of both lungs; a urinalysis shows microscopic hematuria with erythrocyte casts.
Serology is negative for Legionella, Chlamydia, Mycoplasma and Rickettsia.
The renal biopsy shows a diffuse necrotizing glomerulonephritis with crescent formation in ~50% of glomeruli, and smooth linear staining of the glomerular basement membranes.
Sequential bronchoalveolar lavage aliquots reveal the presence of diffuse alveolar hemorrhage.
ANCA: negative for C and P-ANCA ANA titre: undetectable Anti-GBM Abs: present