Introduction:
We present a 51 year old, African American, female who presented with persistent hypoxemia. She had been taking dapsone for many years for prophylaxis against Pneumocystic Jiroveci with no symptoms but eventually developed methemoglobinemia only after a splenectomy. From our literature review there are no documented cases that have demonstrated this relationship between dapsone, splenic function and methemoglobin and we hope to share our perplexing case and shed light on the interaction.
Description:
Our patient has type 1 diabetes and underwent multiple pancreas transplants and an initial kidney transplant during her disease course. One year prior to her presentation she underwent a distal pancreatectomy and an incidental splenectomy during the same procedure. She had been taking dapsone for approximately 17 years due to her allergy to sulfamethoxazole/trimethoprim and her immunosuppressive regimen included tacrolimus, sirolimus, and low dose prednisone. She had presented for a routine, post-surgery follow up visit when she was diagnosed with hypoxemia. After an extensive but unsuccessful work up for persistent hypoxemia, she presented to our clinic for a second opinion. Repeat testing of the arterial blood gas in clinic showed a significant methemoglobin (MHb) level of 16.6 mg/dl.
Discussion:
Although methemoglobinemia is a well-known risk of dapsone exposure, we report a case that suggests that splenectomy can interact with dapsone to further increase the risk of methemobloginemia. We believe that our patient did not develop methemoglobinemia initially, despite being on dapsone for many years because her spleen was able to remove older more susceptible erythrocytes from the circulation leaving the more robust younger erythrocytes. With the splenectomy, the number of older erythrocytes in the peripheral circulation increased and resulted in an accumulation of MHb leading to the low oxygen saturations. Her dapsone was immediately stopped and she was started on vitamin C with a 3 day follow up revealing resolution of her methemoglobinemia and normal oxygen saturation on room air.