Dilantin, an anti-epileptic drug used since the mid-1930s for the treatment of tonic-clonic and partial seizures, has a place on the World Health Organization’s (WHO) List of Essential Medicines.

While phenytoin—its generic name—is not widely prescribed as a first-choice treatment by neurologists, it is still used frequently by general physicians around the globe and in emergency rooms. Alleged phenytoin side effects that affect the area of the brain called the cerebellum may call into question its honored status, however.

These phenytoin side effects are generally associated with long-term use and marked by dramatic changes in patient behavior apparent in gait, eye behavior, speech, and movement of the extremities.

The purported phenytoin side effects are due to the loss of neurons—brain cells—and their connections in the cerebellum. The cerebellum is a lobe of the brain located directly behind the brain stem. The cerebellum is the ‘big coordinator’ of the voluntary muscular system unlike the brain stem which controls the involuntary life processes of respiration and heartbeat.

The alleged phenytoin side effects of cerebellar neuron and overall lobe atrophy are generally first seen in the way a patient ambulates. A sufferer often has a wide spread to his steps and lurches when he walks somewhat like the Frankenstein monster in early horror films. Unlike this image, however, the patient with cerebellar atrophy phenytoin side effects has their arms to their sides and the trunk of the body tends to sway back and forth tremulously.

Eyes may be affected by shrinkage in this lobe with a condition known as nystagmus. With this condition, the iris and pupils of both eyes may dart back and forth from right to left rapidly.

Additionally, cerebellar atrophy may cause the sufferer’s speech to be slurred and memory to be affected. Both symptoms could easily be mistaken for drunkenness to the untrained eye.

Dilantin and Cerebellar Atrophy Studies

It has been long known that both seizure disorders, psychiatric disorders, and some degenerative diseases such as multiple sclerosis can cause cerebellar shrinkage.

Controlling for at least one of these factors, a 1994 study discovered that among seizure disorder patients participating, the half taking Dilantin—or phenytoin—had overall smaller cerebellum. The other half that were not exposed to this drug had larger lobes in this region of the brain.

Another study following up on this finding was released in 2003. It also revealed a strong connection between cerebellar atrophy and long-term use of Dilantin. A link between this atrophy and higher-than-normal blood levels of the drug was also discovered.

Treatment and Recovery

Whether neurons and their connections can be recovered after alleged phenytoin-induced cerebellar atrophy remains unknown. Medically supervised withdrawal from Dilantin is recommended in lieu of patients ceasing to take the drug on their own.

Some recovery has been seen under these circumstances as well as some degree of residual coordination difficulties.