DMSO is used as a cryoprotectant for long-term storage of haematopoietic progenitor cells from the marrow or blood. 1 Until recently, there has been little information on the neurological toxicity of DMSO other than headache. 2 Recent reports suggest that this may be a more frequent problem than currently appreciated. [3][4][5][6][7] A 50-year-old woman developed a Durie-Salmon stage III IgA multiple myeloma in October 2007 and received first-line therapy consisting of thalidomide and dexamethasone. A PBSC collection was performed (highdose CY (4 g/m 2 ) and G-CSF (5 mg/kg/day)). Three million CD34 cells per kilogram were collected. The cells were cryopreserved in 10% DMSO (B. Braun Medical SA, Boulogne, France) using a controlled-rate freezer (Nicool Plus PC, Air Liquide, France) and stored at À150 1C. The final volume cryopreserved was 480 ml in six bags, with approximately 8 g of DMSO per bag (0.13 g/kg DMSO per bag). After PBSC collection, she underwent autologous PBSCT (day 0 ¼ 11 April 2008). The conditioning regimen consisted of melphalan at a dose of 200 mg/m 2 . The bags were thawed in a 37 1C water bath and infused at a rate of 10 ml/min. After the infusion of the last bag, she developed skin pallor, and loss of consciousness (Glasgow Coma Scale 4/15) with hypoxia. Pulse rate was 70/min and blood pressure 120/75 mm Hg. She had no localizing neurological signs. No obvious tonic-clonic activity was noted although she had bitten her tongue and had an evidence of trismus. A seizure was suspected and she was administered with a 15 mg/kg loading dose of phenytoin. The patient was transferred to intensive care unit for ventilation. Blood count, electrolytes, liver function tests and coagulation screen were normal. An urgent brain CT scan was unremarkable. Electroencephalogram showed diffuse abnormalities in the electric activity with irregular paroxysms of slow waves of generalized projection.The patient recovered consciousness in o3 h after assistance ventilation was started. Finally, she was extubated within 24 h, and was discharged from the ICU on day þ 1. She engrafted on day þ 11, and was discharged from our unit on day þ 19. She is now 7 months post transplant, and in CR.Various complications during infusion of cryopreserved haematopoietic stem cells have been described, including nausea, vomiting, cardiac symptoms, transient hypertension or hypotension and anaphylaxis. 8,9 Our patient developed a profound but rapidly reversible coma after infusion of 48 g of DMSO (the equivalent of 0.78 g/kg). She developed this severe complication despite an acceptable dose of DMSO reinfused at a rate generally considered to be safe. The maximal recommended dose of DMSO to be reinfused in one session is 1 g/kg of body weight or 10 ml/kg of a 10% DMSO cryopreserved solution.Other probable causes of seizures, such as metabolic abnormalities, structural brain lesions and sepsis, were ruled out. In the absence of other causes, we attribute the reaction to the DMSO toxicity. Although the pathophysiology of DMSO neurotoxici...