Magnetic resonance imaging for the diagnosis of acute leukoencephalopathy in children treated with tacrolimus

Postnatal toxic and acquired disorders

To develop and function optimally, the brain requires a balanced environment of electrolytes, amino acids, neurotransmitters, and metabolic substrates. As a consequence, organ dysfunction has the potential to induce brain disorders and toxic-metabolic encephalopathies, particularly when occurring during early stages of cerebral maturation. Induced toxicity of three different organ systems that are commonly associated with brain complications are discussed. First, thyroid hormone deficiency caused by intrinsic or extrinsic factors (e.g., environmental toxins) may induce severe adverse effects on child neurological development from reversible impairments to permanent mental retardation. Second, inadequate removal of wastes due to chronic renal failure leads to the accumulation of endogenous toxins that are harmful to brain function. In uremic pediatric patients, the brain becomes more vulnerable to exogenous substances such as aluminum, which can induce aluminum encephalopathy. Following surgical procedures, neurological troubles including focal defects and severe epileptic seizures may result from hypertensive encephalopathy combined with toxicity of immunomodulating substances, or from the delayed consequences of cardiovascular defect. Taken together, this illustrates that organ disorders clearly have an impact on child brain function in various ways.

Medication neurotoxicity in children

Medication neurotoxicity may have a variety of imaging manifestations in children. In this pictorial essay, we review the two most common brain injury patterns, posterior reversible encephalopathy syndrome (PRES) and acute toxic leukoencephalopathy (ATL). Proposed etiologies, salient features on neurological imaging, and methods for differentiating these entities and their implications will be discussed. Certain agents do not fall into these two broad patterns but instead characteristically involve central structures. We individually review several medications and their respective neurotoxic appearances including methotrexate, cyclosporine A, tacrolimus, metronidazole and vigabatrin. Diagnosis of medication neurotoxicity may be achieved by the combination of new-onset neurological deficits, recent initiation of a new therapy agent and distinctive findings on magnetic resonance imaging. Clinical and radiological improvement and/or resolution are frequently observed after the agent is discontinued.

Transient blindness due to posterior reversible encephalopathy syndrome following ephedra overdose

Posterior reversible encephalopathy syndrome (PRES), also known as reversible posterior leukoencephalopathy syndrome (RPLS), is most often associated with hypertensive emergencies and is characterized by seizures, mental status changes and visual disturbances. We report a case of a previously healthy young man who developed multiorgan failure and transient cortical blindness following ingestion of a performance-enhancing ephedra-based supplement. Neuroimaging findings confirmed the clinical suspicion of PRES. Radiographic abnormalities and neurologic dysfunction subsequently resolved with correction of his systolic blood pressure. This case emphasizes the need for prompt treatment and consideration of toxic ingestions in patients presenting with hypertension-related end-organ dysfunction.