Equine leukoencephalomalacia (ELEM), also known as equine mycotoxic encephalomalacia or moldy corn poisoning, is a devastating neurologic disease of horses caused by eating feed or hay contaminated with fumonisin mycotoxins. Fumonisins are produced by 3 species of Fusarium: F. proliferatum, F.verticillioides (formerly F. moniliforme), and F. subglutinans. There are many different types of fumonisins, however the two of most significance include fumonisins B1 and B2. Although many animals and humans are also affected by fumonisin contamination in food, horses are the most sensitive species to fumonisin intoxication, and only have to ingest a small amount to begin showing clinical signs of neurological damage.

ELEM can present in horses in two different forms, which can be neurotoxic and/or hepatotoxic. Usually the neurotoxic form is associated with chronic ingestion of low FB1s and the hepatotoxic form with acute, high-dose exposure. The neurotoxic form is more commonly seen in horses.

The Food and Drug Administration (FDA) in the United States and the European Union Commission have established regulatory limits for the amount of fumonisins that can be present in feeds, corn, and corn byproducts intended for horses; with a maximum of 5 ppm, with the stipulation that the contaminated feed will not constitute more than 20 percent of the horse's diet. Onset of ELEM can occur as early as 7 days after a change in a horse's diet, but usually it takes 14-21 days until clinical signs appear.

Clinical signs

ELEM is difficult to diagnose in horses, which delays treatment and leads to increased fatalities. Usually multiple horses are affected---those consuming the same batch of feed. Horses affected by ELEM die suddenly, with or without the occurrence of clinical signs. When clinical signs do occur, the most common are lost of appetite, lethargy, hypersensitivity and agitation, sweating, muscle fasciculation and weakness, hypermetria, staggering, circling, inability to swallow, blindness, dilated pupils, absence of a pupillary light reflex, head pressing, and tonic-clonic seizures.