Pneumocystis Frequently Found Lethal in Dermatomyositis

The term idiopathic inflammatory myopathy (IIM) denotes a group of autoimmune diseases characterized by myasthenia and typical skin rash, among which dermatomyositis (DM) and polymyositis (PM) are the most common.

Idiopathic inflammatory myopathies (IIM) are associated with a significantly higher risk of opportunistic infections including Pneumocystis jirovecii pneumonia (PJP), a potentially fatal opportunistic infection. In patients with rheumatic immune diseases, most PJP occurs in the first three months after initiating immunosuppressive therapy.

A team of Rheumatologists at the Renji Hospital (Shanghai, China) prospectively followed 463 consecutive patients with IIM a period of at least one year to analyze the incidence of PJP. In the second part of the study, they enrolled 30 consecutive PJP patients with any rheumatic disease in order to identify the mortality rate and risk factors. The diagnosis of PJP was based on comprehensive evaluation by clinical manifestations such as fever or acute dyspnea, characteristic radiographic findings, and etiological evidence. For confirmation, a case needed to have positive microbiological tests such as by next-generation sequencing and Grocott-Gomori methenamine-silver staining of bronchoalveolar lavage fluid.

The team reported that the prevalence of PJP in IIM patients was found to be 3.0/100 person-years, while in anti-melanoma differentiation-associated gene 5 antibody positive (MDA5+) DM patients it was 7.5/100 person-years and in MDA5− IIM patients 0.7/100 person-years. PJP typically occurred in the first two months in the case of MDA5+ DM patients who had a significant decrease in their CD4+ T cell counts and lymphocyte counts. In PJP patients, 3-month mortality was higher for MDA5+ DM patients than in those with other rheumatic diseases (83.3% versus 38.9%). Worryingly, MDA5+ DM patients seemed not to benefit from prompt anti-PJP treatment, unlike patients with other rheumatic diseases whose survival improved when anti-PJP treatment was started within six days.

The authors concluded that the MDA5+ DM patients are highly susceptible to infection with Pneumocystis jirovecii, which is also harder to cure than in other rheumatic diseases. The reason for the higher incidence and mortality may be related to the lower CD4+ T cell counts and progressive interstitial lung disease in MDA5+ patients. The study was published on September 4, 2021 in the journal Arthritis Research & Therapy.

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