Pancytopenia Resulting From Low-Dose Methotrexate Use: A Diagnostic Challenge

Area of Science:

• Rheumatology
• Hematology
• Pharmacology

Background:

• Rheumatoid arthritis (RA) is a prevalent autoimmune disease causing joint erosion.
• Methotrexate (MTX) is a first-line RA treatment due to its efficacy and safety.
• RA treatment complications, including MTX toxicity, require careful management.

Observation:

• A middle-aged female patient presented with severe bone marrow suppression from low-dose MTX.
• Her symptoms mimicked Felty's syndrome and other hematologic disorders.
• A potential drug interaction between piperacillin/tazobactam and MTX was observed.

Findings:

• Corrected reticulocyte count and leucovorin response effectively diagnosed MTX-induced pancytopenia.
• This diagnostic approach avoided the need for bone marrow biopsy.
• MTX toxicity can manifest unusually, even at standard therapeutic doses.

Implications:

• Highlights the importance of considering MTX toxicity in RA patients with cytopenias.
• Provides a practical diagnostic method for MTX-induced pancytopenia.
• Suggests a possible piperacillin/tazobactam and MTX interaction requiring further investigation.