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It is well-known that patients with systemic autoimmune diseases are at risk for Pneumocystis jirovecii pneumonia (PJP) and although infrequent, it carries a high mortality. A new study shows lymphopenia and steroid use increases the risk of PJP.
Prior to 1990 reports were rare, however increasing use of immunosuppression, particularly in combinations, improved diagnostic techniques and awareness of the disease have led to improved documentation.
Unlike in HIV where CD4 counts guide when to initiate PJP prophylaxis, there exists no biomarker in the rheumatology world though there has been a focus on the negative association between lymphocyte counts with PCP occurrence in immunocompromised hosts.
In a recent edition of Seminars in Arthritis and Rheumatism, Tadros et al. presented the results of a case-control study that examined the differences in characteristics and peripheral blood parameters between patients with systemic rheumatic disease who did or did not develop PJP. The authors collected data between 2002 and 2013 from a single center in Melbourne, Australia to match 11 patients identified as having a systemic rheumatologic disease and PJP in a 1:4 ratio with matched controls.
After adjustments for glucocorticoid exposure and CRP, they found that lymphocyte count on admission (0.4 vs. 1.3; p=0.04) and nadir (0.2 vs. 0.8x109/L; p=0.05) were significantly lower in patients with PJP compared to controls.
We know that glucocorticoids are also a risk factor for PJP (and can cause lymphopenia, at least transiently), but this study is the first to show that lymphopenia is a risk factor independent of GC use.
While no consensus guidelines exist, monitoring lymphocyte counts may assist us in deciding when to initiate PJP prophylaxis; although it is unclear what cutoff values should be used.