Delayed Neurological Sequelae of Carbon Monoxide Intoxication Initially Treated as Infectious Meningo Encephalitis.

We report the case of a 75-year-old woman admitted to the emergency department for confusion, gait disturbances and mutism associated with an inflammatory syndrome occurring 3 weeks after acute carbon monoxide intoxication. The main hypothesis upon arrival was infectious meningoencephalitis, and the patient was put on acyclovir and antibiotics in meningeal doses. After a short stay in intensive care, the patient's condition did not improve, and the revaluation of her case history and imaging studies led to the diagnosis of post-interval syndrome secondary to carbon monoxide intoxication after a 3-week asymptomatic period. Post-interval syndrome is a complication poorly known to clinicians, manifesting as neuropsychiatric disorders after carbon monoxide intoxication despite an initial period of improvement. Repeated magnetic resonance imaging, in conjunction with compatible clinical findings, allow the diagnosis to be made. No neurological improved was noted after 6 months follow-up. LEARNING POINTS: Post-interval syndrome is little-known to clinicians and should be considered in any patient presenting with neurological disorders after a symptom-free interval following carbon monoxide intoxication.Repeated magnetic resonance imaging at a distance from the onset of post-interval syndrome (more than a month) helps to distinguish it from cytotoxic oedema which it may be initially confused.The prognosis is poor with no proven effective treatment to date.