Toxic-induced cerebellar syndrome: from the fetal period to the elderly.

The cerebellum is a brain region which is particularly susceptible to intoxication. Clinical presentation is heterogeneous. It is often considered that elderly patients and patients presenting pre-existing structural lesions of the posterior fossa are particularly at risk of developing a toxic-induced cerebellar syndrome (TOICS). However, TOICS may occur at any age, including in utero. Indeed, the cerebellum is highly vulnerable during neurodevelopment. Amongst cerebellotoxic agents, ethanol is the most commonly implicated. The vermis is a privileged target. Ethanol exerts toxic effects upon neurons, glia (especially astrocytes and oligodendrocytes), and myelin sheaths. Prenatal alcohol exposure causes teratogenic effects on the developing cerebellum, impeding neuronal migration and differentiation. In adults, cerebellar ataxia is a major feature of both acute and chronic ethanol intoxication. Wernicke encephalopathy is a medical emergency characterized by a triad of ophthalmoplegia, ataxia, and impaired mental status. It requires the immediate administration of high doses of thiamine by the intravenous route. The following drugs may induce a permanent cerebellar syndrome: phenytoin, lithium salts, antineoplastics, and heroin. In addition to ethanol and drugs, environmental agents are also a source of TOICS. In particular, the cerebellum is susceptible to metal intoxication. The recently described deposits of gadolinium in cerebellar nuclei in patients who had received multiple intravenous administrations are a matter of concern on a worldwide scale but we still lack the demonstration of clinically relevant effects upon motor, oculomotor, or cognitive function. Because cerebellar symptoms may be subtle or immersed in a complex encephalopathy with combined involvement of the peripheral nervous system, the diagnosis of TOICS is often overlooked. The life-threatening risk of edema of the posterior fossa with compression of the brainstem should be kept in mind, including in cases of posterior reversible encephalopathy syndrome, and requires posterior fossa decompression when acute hydrocephalus occurs.