Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis can present with diverse pulmonary manifestations and may closely mimic severe respiratory infection. Interstitial lung disease (ILD), particularly a fibrotic pattern, is increasingly recognized in association with myeloperoxidase (MPO)-ANCA–positive vasculitis. Early recognition of the pulmonary–renal syndrome is crucial to prevent irreversible kidney injury.
A 62-year-old female, Mrs. X, a known case of type 2 diabetes mellitus and hypertension, presented with fever and cough associated with mucoid expectoration for two days, with shortness of breath for one day. On admission, she was tachycardic with a pulse rate of 106/min and tachypneic with a respiratory rate of 32/min. Her blood pressure was 150/90 mmHg, while oxygen saturation was only 60% on room air, indicating severe hypoxemic respiratory failure.
Initial investigations showed hemoglobin of 7.8 g/dL and leukocytosis with a total leukocyte count of 21,230/µL with neutrophil predominance. Renal parameters showed urea 67.6 mg/dL and serum creatinine 3.36 mg/dL. Urine examination revealed 2+ proteinuria and microscopic hematuria. ECG showed sinus rhythm without significant abnormalities. Echocardiography showed normal cardiac chambers, no regional wall motion abnormality and preserved left ventricular systolic function with an ejection fraction of 60%.
CT chest showed subpleural coarse reticulation and honeycombing involving the bilateral lower lobes, predominantly the posterior basal and lateral basal segments. There were areas of cystic bronchiectatic change in the right middle lobe and tubular bronchiectatic changes in the basal segments of both lower lobes. These features were suggestive of fibrotic interstitial lung disease, with a differential of a usual interstitial pneumonia (UIP) pattern versus fibrotic nonspecific interstitial pneumonia (NSIP) pattern. In addition, there were bilateral extensive areas of ground-glass attenuation with a few small patchy areas of sparing, along with mottled irregular consolidative changes involving the right upper and lower lobes. These additional findings were considered suggestive of an infective etiology versus an acute exacerbation of the underlying interstitial lung disease. CT abdomen showed bilateral perinephric fat stranding with normal-sized kidneys and no hydronephrosis.
However, during subsequent follow-up, an important discrepancy emerged. Despite improvement in the total leukocyte count and oxygenation following treatment of the presumed respiratory infection, renal function continued to deteriorate rapidly, with serum creatinine increasing from 3.36 to 5.7 mg/dL within two days. The presence of proteinuria and hematuria, together with rapidly progressive renal dysfunction and pulmonary infiltrates, raised suspicion of a pulmonary–renal syndrome and rapidly progressive glomerulonephritis.
An RPGN work-up was therefore performed, including ANA, anti-GBM antibody and ANCA testing with anti-MPO and anti-PR3 antibodies. The patient was found to have a positive anti-MPO IgG ELISA, supporting MPO-ANCA–associated vasculitis. In the clinical context of rapidly progressive kidney injury and pulmonary involvement, this was considered an ANCA-associated pulmonary–renal syndrome.
Following confirmation of the diagnosis, the patient received intravenous methylprednisolone 500 mg once daily for three days, followed by oral prednisolone at approximately 1 mg/kg/day, with subsequent tapering according to clinical and renal response. Following initiation of immunosuppressive therapy, renal function progressively improved. The patient became clinically better and prednisolone was gradually tapered. On the latest follow-up, serum creatinine had improved to 1.45 mg/dL. She remains on regular follow-up with a tapering glucocorticoid regimen, while appropriate antihypertensive and antidiabetic therapy is continued.
Conclusion: This case highlights the diagnostic challenge of distinguishing infection or acute exacerbation of ILD from ANCA-associated pulmonary involvement. The presence of fibrotic ILD, particularly a UIP-like pattern, may be an important clue to underlying MPO-ANCA–associated vasculitis. Rapidly progressive AKI with hematuria and proteinuria in a patient with pulmonary disease should prompt early evaluation for a pulmonary–renal syndrome. Recognition and timely initiation of immunosuppressive therapy can result in substantial renal recovery.
Think beyond infection in a pulmonary–renal presentation. Pulmonary infiltrates and fever may initially suggest pneumonia or sepsis, but concomitant hematuria, proteinuria and rapidly worsening renal function should trigger evaluation for pulmonary–renal syndrome.
The trajectory of kidney function is a major diagnostic clue. A rapid rise in creatinine over 48 hours, especially despite improvement in systemic infection markers, should raise concern for an active glomerular process.
Urine microscopy is disproportionately valuable. Proteinuria plus hematuria in an unexplained AKI should prompt consideration of glomerulonephritis. Dysmorphic RBCs and RBC casts, if present, would provide further evidence of glomerular bleeding.
CT chest findings are not specific for infection. Ground-glass opacities may occur with infection, pulmonary edema, diffuse alveolar hemorrhage and inflammatory lung disease. Imaging must be interpreted together with renal and serologic findings.
Early recognition can preserve kidney function. The improvement in creatinine from 5.7 to 1.45 mg/dL after immunosuppression highlights the importance of timely recognition and treatment of active AAV.
Infection and vasculitis can coexist or mimic one another. Broad-spectrum antimicrobials may be appropriate initially when infection is plausible, but persistent or disproportionate renal deterioration requires parallel reassessment for vasculitis.
In an adult presenting with apparent pneumonia or sepsis, the combination of rapidly progressive AKI, hematuria and proteinuria should immediately raise the possibility of a pulmonary–renal syndrome. A fall in inflammatory markers or improvement in oxygenation does not exclude simultaneous vasculitis. Early ANCA/anti-GBM testing and, when appropriate, renal biopsy can be decisive. Prompt recognition and immunosuppression in organ-threatening AAV may result in substantial recovery of kidney function.
Dr S Karthikeyan, Postgraduate in Nephrology Kauvery Hospital, Chennai.
Dr R. Balasubramaniyam, Chief Nephrologist and Senior Consultant Kauvery Hospital, Chennai.
