“Natural History” refers to the course of a disease without intervention. In other words, the ‘natural course’ or ‘natural history’. Cervical myelopathy involves compression of the spinal cord. You would think that the natural history of compression on the spinal cord would eventually lead to paralysis. This would be a sensible guess. However, much of the natural history of Degenerative Cervical Myelopathy (DCM) is unknown, including key questions such as how many people worsen, and how quickly?
How Was This Study Performed?
We performed a systematic review to identify all studies that treated patients with DCM without surgery and monitored their outcomes. Out of nearly 10,000 studies that we first screened, we found six that were appropriate to include in the analysis. These comprised a total of 529 patients.
The outcome that the studies were looking for was binary ‘neurologic deterioration’, and this was defined slightly differently depending on the study. We then set out to create a survival curve. These are also referred to as Kaplan-Meier curves and you can see this below. At the left of the curve, we start at 100%, everyone is included. Once a patient deteriorates, they are removed from the curve at that time point. Another way to look at the curve is by looking at the x-axis to find the time point you’re interested in, and the top of the curve at that point tells you how many people have survived. Importantly, we separated out the data into baseline mild and moderate/severe patients assuming they would progress at different rates, which we found to be true.
What Did We Find?
We found that DCM progresses slowly, particularly in mild patients. At 15 years, most mild DCM patients had no neurologic decline. Baseline mild DCM patients have 91% survival at 1 year, 79% survival at 3 years, and 63% at 15 years. This decline slows over time. Baseline moderate/severe DCM patients have 83% survival at 1 year, 64% survival at 3 years, slowly declining to 43% at 15 years.
We published equations to provide an exact estimate of the probability neurologic deterioration below, where ‘S’ represents the likelihood of survivorship (no neurologic deterioration) and ‘t’ represents time in months from today; together the equation represents the probability of not progressing for any given ‘t’.
For patients with mild myelopathy;
and for patients with moderate/severe myelopathy;
Limitations
Despite performing a comprehensive review, we only identified six papers that followed DCM patients without surgery. This may be because of the dogma surrounding operative management of DCM, and this may change.
The studies subjectively defined a minimal objective threshold to state that a patient had definitively declined (usually a 2-point decline on the mJOA). Some factors were not captured, for example, whether the patient subjectively felt worse, or whether the pain had worsened. Part of the focus of future research on DCM is identifying which patients specifically are at a higher risk of progression, and which are lower risk. Our investigation looks at progression on a population level, however, and confirms that the natural history of DCM shows steady albeit slow neurologic decline.
For more, read the full manuscript.
About the Authors
Markian Pahuta, the study’s senior author, is a spine surgeon and associate professor at McMaster University in Hamilton, Ontario. His main research interest is the intersection of health economics and DCM.
Mohamed Sarraj is in his final year of Orthopedic Surgery residency at McMaster University in Hamilton, Ontario. Once finished he will be completing a Spine Surgery fellowship at the Mayo Clinic in Minnesota.