Many patients with spinal cerebrospinal fluid (CSF) leaks, myself included, have encountered the oft-quoted statistic: spontaneous spinal leaks occur in only 5 out of every 100,000 people. This number is frequently used to downplay the likelihood of a leak, particularly after a spinal procedure. However, as with much medical research, it's crucial to delve deeper and understand the study design behind such statistics.
In a previous post within the spinal leak Facebook group I co-moderate, I discussed the importance of critical thinking when evaluating medical research. Today, we'll use this very principle to dissect a fairly recent study on the reported incidence of spontaneous intracranial hypotension, a condition typically secondary to spinal CSF leaks.
Spontaneous Intracranial Hypotension (SIH) as a Misnomer
Before we dive into reviewing the study, we need to clarify some terms. While the term spontaneous intracranial hypotension (SIH) is commonly used, more recent sources–including one listed by the American Society of Anesthesiologists and other pain medicine associations–emphasize that intracranial hypotension is a misnomer and that correct term is actually “intracranial hypovolemia.” Harkening back to the work of the neurologist Dr. Bahram Mokri in the 1990s and early 2000s, the prevailing theory currently is that spinal leaks cause low intracranial CSF volume due to loss of CSF from the spinal leak site. The majority of people with spinal leaks have opening pressures within normal range. Dr. Mokri had hypothesized that intracranial hypovolemia is secondary to a spinal CSF leak and that intracranial hypotension can then sometimes happen as a result of intracranial hypovolemia.
Dr. Mokri had outlined the many manifestations of spinal leaks. There was the typical triad of orthostatic headaches, diffuse pachymeningeal enhancement (DPE) and low opening pressure. However, then there was a broad spectrum from this point that Dr. Mokri recognized, saying “the term CSF hypovolemia is proposed for this syndrome because the term intracranial hypotension no longer seems adequate to embrace all the variations that have emerged.” Within this spectrum, Dr. Mokri pointed to 1) the typical clinical presentation of positional headaches and the typical imaging presentation of diffuse pachymeningeal enhancement (DPE) but yet normal range CSF pressure, 2) the typical clinical presentation of positional headaches and low CSF pressure but yet the absence of diffuse pachymeningeal enhancement (DPE), and 3) the typical imaging presentation of diffuse pachymeningeal enhancement (DPE) and low CSF pressure but yet the absence of a positional headache. Missing here is the additional mention of the typical clinical presentation of a positional headache but yet the absence of DPE which tends to disappear over time and a normal range CSF pressure. More recent research has shown that the absence or presence of DPE correlates significantly with timing of the brain MRI in patients with spinal leaks.
We can view this situation through an understanding of the Monro-Kellie Doctrine, a straightforward principle that asserts that the “combined volume of neuronal tissue, blood, and CSF is constant” and that “to maintain homeostatic intracranial pressure, any increase or decrease in one of these elements leads to a reciprocal and opposite change in the others.” Thus, with greater cerebral blood flow to compensate for low intracranial CSF volume, we can hypothesize that the body would be able to achieve a modicum of homeostasis as far as intracranial pressure which could potentially reduce the headache if the spinal leak were small enough despite causing other symptoms. One such case involved positional unilateral thoracic radiculopathy without a headache, with no DPE visible on brain imaging, and with a normal range opening pressure. Only after a CT myelogram was performed did the researchers find a small leak. The authors thus surmised that the patient’s leak was small enough that her body had been able to compensate, and as a result, she had not experienced headaches. Anecdotally, in cases that I have reviewed as a patient advocate, I found that women with a history of uneventful spinal procedures such as a single-attempt lumbar puncture primarily reported back pain as their greatest symptom.
The Allure of Authority and the Flawed "5 in 100,000" Statistic
With this context, we now return to the aforementioned study. In a sense, spontaneous intracranial hypotension (SIH) could be declared rare as it is rare for people with spontaneous spinal CSF leaks to have low opening pressure. However, the rarity of spontaneous spinal CSF leaks and of CSF hypovolemia can be contested. Spinal CSF leaks as a whole–including spontaneous and iatrogenic–are certainly not rare.
The study, authored by Dr. Wouter Schievink, a leading neurosurgeon at Cedars-Sinai Medical Center, is frequently cited to assert the rarity of spinal leaks. However, a crucial distinction needs to be made: the "5 in 100,000" statistic refers specifically to spontaneous leaks, not those caused by medical procedures (iatrogenic leaks). Unfortunately, this nuance is often lost, leading patients to believe a post-procedural leak is highly improbable.
Let's explore Dr. Schievink's latest research, which investigates the incidence rate within a specific geographic area: Beverly Hills, California, between 2006 and 2020. The study identified a rate of 4 per 100,000 – even lower than the widely quoted 5 in 100,000. On the surface, this reinforces the notion of rarity.
However, a closer look reveals a critical limitation: the sample size. The study analyzed a total of nineteen (19) diagnosed cases of SIH at Cedars-Sinai. This minuscule number raises questions about the generalizability of the findings to a broader population.
Questionable Methodology and Underdiagnosis: A Recipe for Inaccurate Rates
The methodology employed further strengthens the case for critical evaluation. The authors compared the diagnosed cases from specific zip codes with the total population in those areas. This approach disregards the significant number of undiagnosed cases – a well-documented issue with SIH.
Furthermore, the study relied on outdated diagnostic criteria, including opening pressure and pachymeningeal enhancement on brain MRIs. These methods are known to be unreliable for a significant portion of the spinal CSF leak population, particularly in the weeks following leak onset.
Given the limitations in diagnostic techniques during the study period (2006-2020) and the ongoing evolution of diagnosis, the reported incidence rate likely underestimates the true prevalence of SIH.
Beyond the Numbers: The Lived Experience of Patients
While statistics hold a certain weight, anecdotes from patients paint a different picture. Many individuals within the spinal CSF leak community suspect they have a leak despite facing initial dismissal or misdiagnosis. This underscores the need for improved diagnostic tools and a greater awareness of the condition among healthcare professionals.
Moving Forward: Critical Thinking and the Pursuit of Accurate Data
This critical analysis is not intended to undermine the valuable contributions of Dr. Schievink and other researchers. Rather, it serves as a call to action for patients and healthcare professionals alike.
Here are key takeaways:
- Question the Source: Don't blindly accept reported incidence rates. Understand the study design and sample size before drawing conclusions.
- Consider Underdiagnosis: The true prevalence of SIH is likely higher than reported statistics suggest.
- Demand Improved Diagnostics: Advocate for wider adoption of reliable and up-to-date diagnostic methods for spinal CSF leaks.
By fostering a culture of critical thinking and advocating for better diagnosis, we can move towards a more accurate understanding of SIH and ensure timely diagnosis and treatment for patients.
Further Reading:
- Incidence of spontaneous intracranial hypotension in a community: Beverly Hills, California, 2006–2020: https://pubmed.ncbi.nlm.nih.gov/34553617/
Join the Conversation:
This blog post is just the beginning of the conversation. If you're a patient with a suspected spinal CSF leak or a healthcare professional interested in learning more, I encourage you to share your thoughts and experiences in the comments section below. Together, we can raise awareness and advocate for progress in the field of spinal CSF leaks.
