Case Report: MPA Hiding in Plain Sight

Abbreviations not listed in the text: Jo-1 antibody (Ab): anti-histidyl-tRNA synthetase; RNP: ribonucleoprotein; SSA, SSB: anti-Sjögren’s-syndrome-related antigens A and B; SM: Anti-Smith antibody; Scl-70 Ab: Anti-topoisomerase-1 antibodies; ADAMTS-13: ADAM metallopeptidase with thrombospondin type 1 Motif 13

Serological tests are suggestive of a diagnosis; however, guidelines recommend biopsy to confirm the diagnosis of AAV due to its treatment implications.¹³ The ANCA-associated small vessel vasculitis syndromes are referred to as pauci-immune because they show little to no glomerular staining for immunoglobulins or comple­ments on immunofluorescence microscopy. Necro­tizing and crescenteric glomerulo­nephritis are seen on light microscopy, and electron microscopy will show subendothelial edema, microthrombosis and degranulation of neutro­phils without the presence of immune deposits.^10,11

MPA is characterized by non‑granulomatous vasculitis with P-ANCA staining to MPO (~60%). GPA is characterized by necrotizing granulomas with adjacent necrotizing vasculitis. It more commonly presents with C-ANCA to proteinase-3 (~60%), although P-ANCA to MPO can be seen as well (~20%).^9,12

Unlike the pauci-immune pattern of GPA and MPA, Goodpasture syndrome presents with a linear immunofluorescent pattern with anti-basement membrane antibodies. SLE nephritis typically presents with mesangial and subendothelial immune deposits.³ As mentioned above, EGPA typically spares the kidney, but when compromised also leads to the formation of granulomas.

Treatment for the different types of AAV is similar and depends on the presence of organ involvement and the level of disease activity. In the setting of life-threatening organ dysfunction, immunosuppression with pulse dose glucocorticoids and induction with rituximab or cyclophosphamide is recommended.^13,14

Our patient received a course of pulse dose glucocorticoids and rituximab due to the more favorable safety profile when compared to cyclophosphamide. Selected critically ill patients, such as patients with rapidly progressing glomerulonephritis or diffuse alveolar hemorrhage, could be treated with plasmapheresis in the critical care setting, as we opted to do, although a recent randomized clinical trial did not support this.^13,15

Patients, such as ours, often present when they are critically ill, and treatment with immunosuppression should not be delayed. If underlying AAV is a significant concern, treatment should commence immediately, with subsequent biopsy confirmation when possible.¹³

Benjamin Aronow, MD, is an internal medicine intern at the University of Connecticut, Farmington, who will soon start his anesthesiology career at Boston University.

Eduardo Mantovani Cardoso, MD, is an internal medicine resident at the University of Connecticut, Farmington, and will soon be a rheumatology fellow at Beth Israel Deaconess Medical Center, Boston.

Steffi Thomas, DO, is a rheumatology fellow at the University of Connecticut, Farmington.

Prashant Grover, MD, is an assistant professor of medicine at the University of Connecticut, Farmington, and director of the intensive care unit at Saint Francis Hospital, Hartford, Conn.

Weishali Joshi, MD, is a rheumatologist at Saint Francis Hospital, Hartford, Conn.

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