Does Chiari Progress?

June 30th, 2010 - I often decide on what to write about in this column by reading patient posts from various on-line support groups. Recently, I noticed a number of posts by people seeking information on what appears on the surface to be a simple question but actually is not. That question is, "Does Chiari progress?" This question is not only difficult to answer for Chiari but when you think about it, also difficult to answer for a number of other diseases and medical conditions as well.

What makes this question difficult to answer in the case of Chiari is that there can be a lot of variation between patients. There are differences between groups like children and adults as well as differences between individuals. In children, natural growth can change the anatomy of the malformation for better or for worse. In adults, aging, trauma, medications, diseases that affect the spine like arthritis and osteoporosis, and even events like child birth can result in permanent or transient anatomical changes that can affect symptoms.

Another important consideration is the phase of the condition. When answering this question, it is important to be specific. Asking if the condition will progress in patients with herniated tonsils but who have no symptoms is an entirely different question than asking if progression will occur in patients already experiencing symptoms.

Definitions are also important to consider particularly in patients without symptoms. People with herniated tonsils and no symptoms may never become symptomatic and thus should probably never be labeled as Chiari patients in the first place. This has to do with definitions. At present, there is a tendency to define Chiari on the basis of the length of herniation. Unfortunately, the length of herniation does not correlate well with symptom severity. Symptom severity depends in part as to whether or not the herniated tonsils impede the drainage of cerebrospinal fluid from the skull. Whether or not the tonsils impede flow depends on the overall shape of the tonsils and other factors and not the length of the tonsils alone. Some people can have significant herniation lengths but still have sufficient space at the base of the skull to permit normal drainage and they can remain that way for the rest of their natural life. While little data exists on the natural history and progression of Chiari, the evidence that does exists seems to suggest that most people with tonsil herniations will never become symptomatic. Ideally, we would like a definition of the disease and diagnostic measure of the condition such that symptomatic progression is highly predictable but that doesn't exist at present.

There only exists in the medical literature a couple of studies on the natural history of Chiari1,2. In all cases, the studies are too small and too short in observation time to make firm conclusions. Also, these studies followed patients who were asymptomatic and whose malformations were found incidentally following head MRIs taken for other reasons. These studies show that about 10-15% of these patients will progress to a symptomatic state requiring surgical decompression.

Unfortunately, most people who ask about the progression of Chiari are those with existing symptoms and no published studies on the natural history and progression of Chiari in patients with existing symptoms exist. It is extremely important to recognize that the progression of symptoms in asymptomatic and symptomatic patients can not be assumed to be similar. In fact, anecdotal observations suggests that it is very different and that symptom severity more frequently increases in symptomatic patients. However, this anecdotal observation is clouded by the fact that the severity of symptoms in symptomatic patients is often masked by treatment with drugs. And, herein lies a major problem and concern. Symptomatic patients being treated with drugs are at risk of long term drug side effects as well as silent progression of the disease that can lead to further neurological damage including syringomyelia.

So, one question that emerges is, "If progression is likely more common in symptomatic patients then why do so many doctors tell patients that Chiari doesn't progress or rarely progresses?". Well, like the last question, it depends, It depends on the specialty of the doctor, the doctor's personal experience with Chiari, the manner in which doctors manage risk, the doctor's communication style with patients, and even the doctor's approach to managing his/her practice as a business.

When it comes to Chiari there is a distinct difference between neurologists and neurosurgeons. Neurologists primarily treat patients with either drugs or physical therapy, not surgery. Chiari doesn't respond well to drug treatment. As a result, Chiari patients end up at the neurosurgeon's office and neurologists see less of them and therefore don't take the initiative to learn more about the disease.

Many neurologists have also been trained in the trenches as opposed to the class room when it comes to Chiari and in this training environment have been taught incorrectly that Chiari is not a real disease but an asymptomatic malformation of the brain that is actually a variant of normal. Consequently, they believe that patients with herniated tonsils that complain about symptoms not explained by other diseases are suffering from depression or mood disorders. They tell these patients that Chiari really isn't responsible for their complaints and often prescribe pain medications or antidepressants. Another possibility is that they will misdiagnose them with diseases like fibromyalgia and refer them to a different specialist or treatment with medications like Lyrica. Actually, in many cases, they may be right but in certain cases they may be wrong.

When it comes to neurosurgeons, the spectrum of response is considerably wider. Some respond like the neurologists above but not as many. Others do a more thorough work up that includes diagnostic tests such as Cine MRI and a complete MRI of the spine. When these neurosurgeons arrive at a diagnosis of symptomatic Chiari on the basis of clinical findings and Cine MRI, their recommendation regarding decompression surgery can vary. Many will prefer to wait and observe for a period of time. Why? Because decompression surgery has a relatively high failure rate. Only about 20% will experience a significant improvement while about 50 to 60% will not experience improvement. The remaining fraction of about 20% will continue to worsen. Also, even in symptomatic patients, progression is variable. Many will not grow worse and a small fraction may improve with time. As a result, many neurosurgeons take a wait and see approach even with patients chomping at the bit so to speak for surgical treatment. And, importantly, when they recommend surgery they stress that they can not promise improvement with their goal or definition of success being an outcome where no further progression will occur.

So, where does all of this net out? For patients without symptoms who learn they have Chiari as a result of tonsil herniation being discovered incidentally, the scant data in the literature suggests that most of them will not progress to a symptomatic stage. For patients who are symptomatic, it is important first of all to get a complete work up that includes Cine MRI and an MRI of the full spine. Those who do not get a Cine MRI and full spine MRI and who walk away without a clear diagnosis for the cause of their symptoms should not be satisfied and should continue to seek other opinions until a clear diagnosis is reached. For those who receive a diagnosis of symptomatic Chiari and whose symptoms interfere with their normal standard of living, decompression surgery should be considered. For those whose symptoms are mild to moderate, there is a distinct probability, although impossible to quantify, that their symptoms may worsen. For these individuals, a wait and see approach may be warranted taking care not to cloud the picture going forward with too much drug treatment. Keep in mind that an increase in the use of medication to manage symptoms is often a sign of worsen disease.

Chiari varies greatly across individuals. The anatomy of each patient's malformation is different. Patients also vary in their underlying health condition. Symptom progression can occur but it is not possible to predict to what extent it will occur or how fast. Current evidence which is inadequate suggests that symptomatic patients are more likely to worsen than asymptomatic patients. Finally, the decision to proceed with decompression surgery depends on several factors including but not limited to the severity of symptoms, objective evidence that cerebrospional fluid drainage is impeded, the clinician's confidence that symptoms can not be attributed to other diseases or conditions, and the patient's overall health status.

1J Neurosurg Pediatr. 2008 Sep;2(3):179-87.
Neurosurgery. 2001 Sep;49(3):637-40

Ed. Note: The opinions expressed above are solely those of the author. They do not represent the opinions of the editor, publisher, or this publication. Mr. D'Alonzo is not a medical doctor and does not give medical advice. Anyone with a medical problem is strongly encouraged to seek professional medical care.