Summary

A 5-year-old boy from the Congo, was admitted for hyperleucocytic acute lymphoblastic leukaemia, with a high risk of tumour lysis syndrome (TLS). He had splenomegaly and mediastinal lymphadenopathy on chest X-ray. We started steroids and hyperhydration with rasburicase to prevent TLS. Respiratory failure with mediastinal enlargement developed rapidly. A few hours after intensive care unit (ICU) admission, he was started on mechanical ventilation. Chemotherapy was started immediately given the strong suspicion of mediastinal compression. Low oxygen saturation with high partial arterial oxygen pressure persisted. Blood tests confirmed 20% methaemoglobinaemia and glucose-6-phosphate dehydrogenase (G6PD) deficiency. Allopurinol was substituted for rasburicase. The methaemoglobinaemia disappeared rapidly and he was discharged from the ICU after 72 h. In case of rasburicase use, a close clinical monitoring is mandatory, especially in populations where G6PD deficiency is highly prevalent. Methaemoglobinaemia must be suspected in case of low oxygen saturation when all other potential causes have been ruled out.