# Mycobacterial Infections in Patients With Hairy Cell Leukemia: A Systematic Review of Published Cases

## TL;DR

This study reviews mycobacterial infections in patients with hairy cell leukemia, finding that these infections are often severe and widespread, with high mortality rates.

## Contribution

The paper provides the first systematic review of mycobacterial infections in hairy cell leukemia, highlighting clinical patterns and outcomes.

## Key findings

- Mycobacterial infections in HCL are frequently disseminated and associated with substantial mortality.
- Nontuberculous mycobacteria, particularly M. kansasii and M. avium complex, are the most common causes of infection.
- Pulmonary involvement is associated with significantly higher mortality rates in these patients.

## Abstract

Hairy cell leukemia (HCL) is a rare B-cell lymphoproliferative disorder characterized by monocytopenia and profound defects in cellular immunity, predisposing patients to severe mycobacterial infections. Although numerous case reports exist, the clinical features and outcomes of these infections have not been systematically synthesized.

We conducted a systematic review following PRISMA guidelines, searching PubMed, Embase, and Web of Science from inception to 31 January 2025, without language restrictions. Studies were eligible if they contained individual patient-level data on microbiologically confirmed mycobacterial infection in HCL. Data on demographics, clinical presentation, organ involvement, pathogen distribution, treatment timing, and outcomes were extracted and analyzed descriptively.

Thirty-six articles describing 48 patients met the inclusion criteria. The mean age was 53.7 ± 12.7 years, and 39/48 (81%) were male. Disseminated infection was common, occurring in 34/48 (71%) cases, with frequent involvement of lymph nodes (60%), lungs (56%), liver (27%), spleen (25%), and bone marrow (19%). Infections were caused by Mycobacterium tuberculosis complex in 12/48 (25%) and by nontuberculous mycobacteria in 33/48 (69%), most commonly M. kansasii (55%) and M. avium complex (30%). Overall, 19/48 (40%) patients died, with significantly higher mortality among those with pulmonary involvement (79% vs 41%; P = .01).

Mycobacterial infections in HCL are frequently disseminated and associated with substantial mortality. Clinicians should maintain a high index of suspicion, ensure timely species-level diagnosis, and evaluate for multisystem involvement when managing suspected mycobacterial disease in HCL.

This systematic review synthesizes published cases of mycobacterial infections in hairy cell leukemia, demonstrating frequent dissemination, predominance of nontuberculous mycobacteria, and substantial mortality. Early clinical suspicion, timely species-level diagnosis, and comprehensive evaluation are critical to improving outcomes in this highly immunocompromised population.