Polymicrogyria (PMG)


Polymicrogyria (PMG) is a condition characterized by abnormal development of the brain before birth. While a baby is still in the womb, brain cells called neurons are migrating to where they are supposed to go. For some reason, the neurons become disorganized and land in the wrong places. The surface of the brain normally has many ridges or folds, called gyri. In children born with Polymicrogyria, the brain develops too many folds, and the folds are unusually small. The name of this condition means too many (poly-) small (micro-) folds (-gyria) in the surface of the brain.

The area of the brain involved by the polymicrogyria typically does not function normally. The impairments depend on what parts of the brain are involved and how severe the deformity is. Sometimes polymicrogyria may affect only a portion of one hemisphere, but at other times can affect one entire hemisphere or be seen in both hemispheres. If seen on both sides, sometimes the changes are quite diffuse throughout the brain but at other times can affect a predominant region of both hemispheres (such as bilateral perisylvian polymicrogyria).

Other names for PMG include: classic PMG, cobblestone malformation, tubulinopathy-associated dysgyria.

There are several known causes for polymicrogyria. The most common of which results from the virus cytomegalovirus (CMV). Other causes include various prenatal infections, brain abnormalities, genetic disorders, and more.

This condition may also result from brain injury while a baby is still in the womb. This is due to low blood flow or infection (such as CMV). Some cases may also be due to metabolic disorders like Zellweger syndrome. Problems can stem from how the brain breaks down nutrients leading to lack of a crucial substance or buildup of a toxic substance.

Approximately 90% of persons with polymicrogyria develop seizures at some point in their life, and most of these will begin in childhood. In those who do develop epilepsy, several types of seizures can be seen, based upon the location, severity, and type of disorder itself.

Polymicrogyria affecting a smaller area of one hemisphere (side of the brain) often presents with focal seizures in children or slightly older individuals, many of whom have been otherwise healthy. Sometimes these focal seizures can spread to involve both sides of the brain and thus appear a generalized tonic-clonic seizure.

Polymicrogyria that involves one entire hemisphere (side of the brain) is usually associated focal seizures affecting the opposite side of the body that begin in early to mid-childhood, weakness and movement problems on that side of the body, and mild to moderate intellectual disability.

Persons with bilateral polymicrogyria often have atypical absence seizures, tonic or atonic drop attacks and tonic-clonic seizures in addition to focal seizures, and can sometimes present as Lennox-Gastaut syndrome. Some of these babies can also start having infantile spasms earlier in infancy.

Common symptoms and comorbidities to Polymicrogyria are:

  • Cerebral Palsy
  • Motor delays
  • Cognitive and emotional delays
  • Speech delays
  • Swallowing problems
  • Abnormal head size (too big or too small)

Common cognitive or intellectual disorders connected to PMG include:

  • Speech and motor function delays
  • Autism
  • Behavioral delays
  • Dyslexia

Polymicrogyria is diagnosed by brain magnetic resonance imaging (MRI), which will show the abnormal brain structure and provide information on the location and extent of the abnormality.

In persons with seizures, an EEG can be helpful to confirm the seizure type(s). Persons with PMG should also be considered for genetic testing, as a number of genes have been associated with this brain change.

We do not know exactly how common this condition is, however it is vital to diagnose. PMG is often a cause of drug-resistant epilepsy. Knowing the cause helps guide the treatment programs available.

The Polymicrogyria (PMG) malformation cannot be reversed, but the symptoms may be treated in children and adults. The first-line treatment for persons with seizures is anti-seizure medications, and the medication chosen depends on the type of seizures or epilepsy syndrome. Persons who continue to have seizures despite trials of two or more anti-seizure medications should be considered for referral to a comprehensive epilepsy center.

Persons with polymicrogyria affecting a small region of one hemisphere could be considered for resective surgery, and those with unilateral hemispheric involvement can be considered for hemispherectomy. In general, persons with bilateral polymicrogyria are not good candidates for epilepsy surgery, but may benefit from dietary treatment with a ketogenic diet, or from neuromodulation, such as vagus nerve stimulation (VNS), deep brain stimulation (DBS) or responsive neurostimulation (RNS). Many persons will also benefit from occupational, physical, and speech therapies.

What is the outlook for Polymicrogyria (PMG)?

Disclaimer: This field is rapidly evolving, and each individual has their own course. We are constantly learning, and published data may be slow to come.

Children with polymicrogyria will grow up to become adults with polymicrogyria. It cannot be outgrown. It is a lifelong disorder characterized by irreversible, abnormal brain development. Not all patients will develop epilepsy. For those who are candidates for surgical treatment or hemispherectomy, seizures may abate after surgery; however, those are the minority of cases. Many persons will have a life-long predisposition to seizures.

Authored By:

Cody Stevens

on Sunday, April 04, 2021

Reviewed By:

Dr. Ghayda Mirzaa MD
Elaine Wirrell MD

on Sunday, April 04, 2021


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