Non-lymphopenic pneumocystis pneumonia in low-dose methotrexate therapy: An exception to every rule

Area of Science:

• Infectious Diseases
• Rheumatology
• Immunology

Background:

• Pneumocystis jiroveci pneumonia (PCP) is a significant opportunistic infection in immunocompromised individuals, particularly those with rheumatic diseases.
• PCP is often linked to lymphopenia and elevated serum lactate dehydrogenase (LDH) levels.
• The risk of PCP generally correlates with the dosage of immunomodulatory drugs used to manage underlying conditions.

Observation:

• This report details a case of PCP in a patient diagnosed with psoriatic arthritis.
• The patient was undergoing treatment with a low dose of methotrexate.
• Notably, the patient did not present with lymphopenia, a common characteristic of PCP.

Findings:

• Pneumocystis jiroveci pneumonia (PCP) occurred in a patient with psoriatic arthritis.
• The patient was on low-dose methotrexate therapy.
• The absence of lymphopenia in this case deviates from typical PCP presentations.

Implications:

• This case expands the understanding of PCP risk factors beyond lymphopenia and high-dose immunosuppression.
• It suggests that patients with psoriatic arthritis on low-dose methotrexate may be at risk for PCP, irrespective of lymphopenia.
• Clinicians should consider PCP in immunocompromised patients with rheumatic diseases presenting with atypical features.