Abstract Introduction Dermatomyositis is a rare idiopathic inflammatory myopathy frequently complicated by interstitial lung disease (ILD), a major contributor to morbidity and early mortality. ILD occurs in up to one-third of dermatomyositis patients and may precede or occur independently of classic muscle or skin findings. Certain autoantibodies, such as anti-MDA5, are strongly associated with rapidly progressive ILD and poor prognosis. Presentation is heterogeneous, and early recognition is essential. This case describes a patient with rapidly progressive ILD who initially presented with Pneumocystis jirovecii pneumonia (PJP) and recrudesced after steroid cessation, ultimately diagnosed with dermatomyositis. Case A healthy 50-year-old man presented with a 4-month history of fatigue, 30-pound weight loss, intermittent dysphagia, exertional dyspnea, dysphonia and fissured lesions around his mouth, elbows, and hands. Imaging revealed bilateral interstitial and ground-glass infiltrates. His respiratory status deteriorated rapidly, requiring ICU transfer and intubation. BAL was positive for PJP. CD4 count was low, but HIV was negative. Infectious and autoimmune workup for underlying etiology was initially unrevealing. He was treated for PJP with trimethoprim-sulfamethoxazole and prednisone and was discharged to rehabilitation.Four weeks after cessation of steroids, he developed a facial rash and re-presented with worsening hypoxemia. Repeat infectious workup was negative. Multidisciplinary consultation identified Gottron’s papules and worsening ILD. Myositis-specific antibody panel was positive for anti-MDA5, confirming dermatomyositis. He was started on tacrolimus, IVIG, rituximab, and methylprednisolone, with sustained clinical improvement. Discussion This case highlights the profound immunocompromised state induced by dermatomyositis, particularly anti-MDA5-positive disease, and resultant ILD presenting as PJP. Emerging evidence indicates that underlying autoimmune diseases themselves may confer substantial risk for PJP independent of immunosuppressive therapies. Studies show that dermatomyositis is an independent risk factor for PJP, with anti-MDA5 antibodies, lymphopenia, and concurrent viral infections shown to amplify risk. The pathogenesis may relate to defects in cellular immunity, particularly in anti-MDA5+ subtypes, characterized by lymphocyte depletion and impaired host defense. The patient’s initial clinical improvement following therapy was consistent with the expected response to PJP-directed treatment. However, it is important to note that after cessation of steroids, the patient experienced recrudescence of ILD, manifesting as worsening hypoxemia and facial rash.This case underscores the importance of considering dermatomyositis in the differential diagnosis of PJP-positive acute respiratory failure, especially when lymphopenia or ILD is present. Early recognition and intervention are essential, as timely anti-PJP therapy may not fully mitigate the high mortality associated with dermatomyositis related PJP, particularly in anti-MDA5+ cases. This abstract is funded by: none
Elashker et al. (Fri,) studied this question.