Dilantin—known generically as phenytoin—has been successfully used to treat certain types of seizure disorders since its debut in the late 1930s. Symptoms of cerebellar atrophy, however, have been correlated in recent years with the long-term use of the drug.

These long-range Dilantin side effects are often observable in patients through changes in their ability to maintain balance and through changes in the way they ambulate and talk.

Symptoms of Cerebellar Atrophy

The cerebellum is a bilateral lobe of the brain located behind and near the base of the brain stem. It is responsible for coordinating voluntary muscle movements from different areas of the body to complete complex tasks such as ice skating, playing tennis, or going on a cross-country run.

It is also responsible for a more delicate balance, timing, and organization necessary in everyday speech, walking, and attention to sensory input.

Dilantin side effects that are symptoms of cerebellar atrophy might be first visible with an unusual gait. The gait is often described as both tentative and lurching. The ambulatory symptoms of cerebellar atrophy may be accompanied with a back and forth tremor of the middle part of the body—the trunk or torso.

Dilantin side effects related to the shrinkage of the cerebellum may not be limited to the manner in which a patient walks, however. Symptoms of cerebellar atrophy include a particular kind of eye behavior which can appear shifty and or sinister to the untrained observer. This eye behavior is called nystagmus and is an involuntary side-to-side movement of the eyes that is technically part of the voluntary motor control center.

Two other areas where symptoms of cerebellar atrophy reveal themselves are in speed of thought processing and the manner in which a patient speaks. Long-term use of Dilantin can lead to a slow hesitation when processing communication and responding.

The hesitation is also present in speech and can be accompanied by a slurring reminiscent of drunkenness. Again, to the untrained observer, Dilantin side effects can mock alcoholic inebriation.

Does Long-Term Use of Dilantin Cause Permanent Cerebellar Atrophy?

One of the difficulties in assessing the correlation between long-term use of Dilantin and cerebellar atrophy is that the presence of a seizure disorder has been known to cause shrinkage to this lobe in and of itself. Back in 1994, a study was completed that controlled for this fact.

The enrollees in this study all had seizure disorders, but half were treated with Dilantin and the other half treated with another anticonvulsant medication. Both the treatment recipients and the researchers were blind as to which drug was being administered in each case.

When data was evaluated at the conclusion of the study alongside Magnetic Resonance Imaging (MRI) information, it was apparent that epilepsy patients that had taken Dilantin long-term had much smaller cerebellums when considering the average.

It is unknown as to whether the neural connections that contribute to the lobe’s size can be regained if the treatment regimen is changed from Dilantin to another anticonvulsant drug. Improvements have been seen in patients, however, that have made a switch.

It is important to note that because seizures are serious and potentially life-threatening, a change in medication should always be done under the advice and guidance of the prescribing physician.