Hereditary methaemoglobinemia caused by haemoglobin M Boston

On March 29, 2020, a 26-year-old man presented to our hospital with hydronephrosis found on physical examination. On admission, the patient was found to have cyanotic skin and lips (figure). The physical examination showed no other abnormalities, including symptoms such as chest tightness, asthma, or dyspnoea after climbing stairs or doing other activities. His fingertip oxygen saturation ranged from 35% to 40% as measured by a finger cuff photoelectric sensor; even at an oxygen concentration of 35%, his fingertip oxygen saturation was 57%. Arterial blood gas analysis showed that his oxygen saturation was 57%, oxygenated haemoglobin concentration was 79·8%, reduced haemoglobin concentration was 11·4%, methaemoglobin concentration was 7·6%, and haematocrit concentration was 48·2% (appendix p 1). His blood cell analysis, chest CT, and cardiac ultrasound were normal. After confirming that his cardiopulmonary function was normal, we did ureteral stenting under epidural anaesthesia to relieve his hydronephrosis, and the patient's onset time of anaesthesia was approximately 30 minutes after epidural administration. The operation was successful, and the patient was stable during surgery. During venous blood sampling, we observed that the patient's blood was chocolate coloured (figure) and that the blood did not change colour in the air. The patient and family members reported that the patient had had cyanotic skin, lips, and nails from an early age but had no discomfort or other symptoms, and his life and work were not affected; therefore, no treatment was administered for this symptom. His parents were not consanguineous, and his father and brother had similar symptoms without other abnormalities. We investigated his family and found that the proband's grandmother, uncle, and two cousins had cyanosis but his other relatives did not. When we investigated his community, we found that there was another local family with similar symptoms, and according to the two individuals, their two families were related through a common ancestor (appendix p 2).