SULFHEMOGLOBINEMIA: SULFURING FROM A RARE CONDITION Kaitlin V. Bradley DO MS, Richard D. Cornwell MD, Hilary Faust MD

INTRODUCTION: Sulfhemoglobin is a rare dyshemoglobin resulting from incorporation of sulfur into the oxidized form of iron in the hemoglobin moiety. Sulfhemoglobin is unable to bind oxygen for the life of the erythrocyte, leading to discrepant pulse oximetry and arterial oxygen tension (PaO2). Oxygenation of the tissues is only mildly affected due to the right shift of the oxy-hemoglobin dissociation curve for the remaining oxyhemoglobin molecules. Occupational exposures, medications, and sulfide-producing intestinal flora have been implicated in its development. Sulfhemoglobin and methemoglobin share similar presentations of cyanosis, hypoxia without hypoxemia, and absorptive peak wavelengths on co- oximetry, and thus distinguishing the difference can be a diagnostic challenge.

CASE PRESENTATION: A 64-year-old female with recent initiation of ferrous sulfate for anemia, Lynch syndrome s/p hysterectomy, abdominal peritoneal resection and pelvic radiation, multiple bowel obstructions s/p end colostomy, and newly diagnosed colonic adenocarcinoma with colovesicular fistula, presented with concern for bowel obstruction. Room air pulse oximetry was around 80% and unresponsive to oxygen. CT PE study demonstrated segmental and subsegmental pulmonary emboli. Anticoagulation was started and she was admitted for exploratory laparotomy. Arterial blood gases on nasal cannula, high flow nasal cannula and CPAP, all demonstrated preserved arterial oxygenation discordant with low observed pulse oximetry. Further workup with TTE, methemoglobin levels, and hemoglobin electrophoresis were normal and a pulmonary consult was requested for preoperative evaluation. Specialized testing sent to Mayo revealed elevated sulfhemoglobin at 3.5%. Ferrous sulfate was discontinued and the patient underwent surgery. Unfortunately, due to inability to fully resect the colonic mass, the patient pursued comfort measures.

DISCUSSION: Sulfhemoglobinemia is a rare dyshemoglobinemia reported in conjunction with medications, bowel pathology and occupational exposures. In our patient, ferrous sulfate was the most likely precipitant, but multiple predisposing conditions including colonic malignancy, fistula and previous intra-abdominal surgeries may have contributed. Therapeutic management presents a unique challenge due to the irreversible binding of sulfur to the hemoglobin moiety and lack of response to methylene blue or other antidotes. Treatment focuses on removing the offending agent with repeat evaluation after roughly 120 days. Exchange transfusions can be considered for severe cases.

CONCLUSIONS: Sulfhemoglobinemia is a rare but likely under-recognized clinical entity. Given the ubiquitous nature of sulfur-containing medications, the diagnosis should be considered in patients with discordant pulse oximetry and arterial oxygen saturations.

REFERENCES:  Derbas L, et al. BMJ Case Rep 2017. doi:10.1136/bcr-2017-220521  Askew, Stephen et al. On the dysfunctional hemoglobins and cyanosis connection: practical implications for the clinical detection and differentiation of methemoglobinemia and sulfhemoglobinemia. Journal of Biomedical Optics Express. 2018 July, Vol. 9, No. 7  Noor M, Beutler E. Acquired sulfhemoglobinemia. an underreported diagnosis? West J Med 1998;169:386–9