[A rare cause of cyanosis: Sulphaemoglobinaemia related to thiocolchicoside (Miorel)].

Introduction: An acquired abnormality of haemoglobin is among the many causes of cyanosis, especially in patients with no identified cardiorespiratory cause.

Case Report: A 50-year-old woman, suffering from amyotrophic lateral sclerosis, was hospitalised for dyspnoea. Physical examination revealed cyanosis that persisted despite oxygen therapy. Discordance between the reduced arterial oxygen saturation and normal arterial oxygen tension led to a search for a dyshaemoglobinaemia as a possible cause. Use of co-oxymetry with spectrophotometry revealed sulphaemoglobinaemia. Sulphaemoglobinaemia is due to irreversible incorporation of a thiol radical into the porphyrin ring of a haem group. This decreases the affinity of haemoglobin for oxygen and thus reduces oxygen carrying capacity. A drug-induced cause is often identified. However, no previously described cause for sulphaemoglobinaemia was identified in our patient. The patient was currently being treated with thiocolchicoside (Miorel((R))). Thiocolchicoside was suspected as the cause because its chemical structure contains an easily hydrolysable thiol radical. Withdrawal of thiocolchicoside led to regression of the sulphaemoglobinaemia.

Conclusions: This report underlines the importance of searching for an acquired abnormality of haemoglobin (methaemoglobinaemia or sulphaemoglobinaemia) in patients with cyanosis resistant to oxygen, in the absence of any cardiorespiratory abnormality. This case is the first to suspect thiocolchicoside as a possible cause of sulphaemoglobinaemia.