Anti-Glomerular Basement Membrane Disease Sans Kidney Involvement

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Introduction: Anti-Glomerular Basement Membrane (anti-GBM) is an autoimmune disease involving glomerular and pulmonary capillaries diagnosed in 1 patient per million per year. Predominant lung involvement can be seen in 6% of patients most of which still demonstrate microscopic hematuria and biopsy with typical linear IgG immunofluorescence (99%). Case Description: We report a case of a 57-year-old man who presented with several weeks of dyspnea and myalgia, and was found to have acute kidney injury and multifocal tree-in-bud groundglass opacities throughout both lungs (Figure 1). His serum creatinine was elevated to 4.5 mg/dL from baseline of 0.8 mg/dL three months earlier but no proteinuria or hematuria. COVID19 was negative. Bronchoscopy showed blood throughout the tracheobronchial tree. Anti-GBM was elevated at 80 AU/mL. CRP was elevated at 17 mg/dL. Further work-up for other infectious or autoimmune causes was unremarkable. Kidney biopsy showed acute tubular necrosis (ATN), mixed interstitial inflammatory infiltrate, and one isolated fibrous cellular crescent. Immunofluorescence was negative. Due to the concern for progression of untreated anti-GBM disease, the patient was given high dose steroids, plasma exchange, and oral cyclophosphamide. His anti-GBM titer decreased to an undetectable level. Creatinine improved to 2.33 mg/dL. Discussion: This case brings to light a rare variant of anti-GBM with no detectable kidney involvement and presents a therapeutic dilemma. Two independent pathologists reviewed kidney biopsy and felt that crescent was a non-specific result of prior glomerular injury or pauci-immune focal glomerulonephritis. ANCA serologies were negative, and there were no other systemic manifestations. ATN was attributed to poor intake and Naproxen use. The patient received a typical anti-GBM treatment but more data are needed to support this approach in mild cases.

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