MSFinals-2077

A 50-year-old male has a history of severe rheumatoid arthritis for the past four years. Despite being compliant with therapy (NSAIDs and methotrexate), the disease remains poorly controlled. Recently, he has been experiencing extreme fatigue. Upon conducting an FBC, the following results were obtained:
– Haemoglobin 70 g/L (120-160)
– White cell count 1.5 ×109/L (4-11)
– Platelet count 40 ×109/L (150-400)

What could be the possible cause of his pancytopenia?