Proponents of irregular medicine love anecdotes and testimonials. They love them because humans are somewhat unique in the animal kingdom in that we are particularly impressed with personal stories, at least much more so than pangolins and dugongs in my experience. It is simply an unfortunate side effect of our highly developed prefrontal cortex that we place more emphasis on a compelling narrative than on randomized controlled trials.
But when it comes to bridging the gap between infinitesimally plausible interventions and scientific street cred, nothing beats the case report. Surely a poorly designed trial involving multiple human subjects is more impressive, especially when it confirms what you already believe, but these are expensive and time consuming. Much more bang can be extracted from the potential patient per buck with a good story, especially if it’s published in an actual (wink wink nudge nudge) medical journal. Now that I think about, it’s actually the bucks that are being extracted.
To be fair, a case study documented with attention to scientific detail and appropriate context, as opposed to the typical anecdote or testimonial, can have considerable value, even if it should rarely if ever be used to justify claims of a causal nature. They can serve the purpose of disproving an all-inclusive assumption. They can help to guide future research. And if a condition is extremely rare, they might be relied upon for determining an approach to treatment. The case report is best utilized, in my opinion, as a hypothesis generator or even as an educational tool.
Chiropractors love case reports! Maybe not this one though
In prior posts, particularly this one on spinal adjustments as a treatment for Tourette syndrome, I’ve discussed case reports published in the chiropractic literature. These case reports are legion and commonly used to promote the use of chiropractic manipulation to treat non-musculoskeletal conditions. They are almost exclusively published in journals that focus on chiropractic or alternative medicine in general, and frequently demonstrate a fundamental ignorance of the pathophysiology and expected natural course of the condition being treated.
This week a case report of a different color was published in The American Journal of Ophthalmology Case Reports. The authors describe in detail, with cool pictures included in the report, the case of a 59-year-old woman who developed spots in her vision while driving home from a visit to her chiropractor. During the visit, high-velocity, low-amplitude (HVLA) adjustment of her neck was performed.
Although not made clear in the report, it appears that she had sought chiropractic evaluation and treatment for her history of headaches and/or restless leg syndrome. It is possible that she had sought out a chiropractor for help with her psoriasis, but that would be pretty unlikely. I mean, they would never claim to be able to manage psoriasis. Right?
Unfortunately, of course they would.
The patient found her way to a retinal specialist at University of Michigan’s Kellogg Eye Center where she was found to have multiple preretinal (vitreous) hemorrhages, with one over the optic nerve, and a posterior vitreous detachment. After a thorough investigation, they were unable to find any reason for the findings other than trauma. And taking into account the timing of her presentation and the known forceful nature of HVLA neck adjustments, they came to the same conclusion that any rational person would.
Ocular risks from chiropractic adjustments
As has been discussed several times before on SBM, there are uncommon but potentially quite deadly risks when it comes to aggressive neck adjustments. I’m talking about injury to the vertebral artery and subsequent stroke. When a blood vessel in the neck is injured and bleeds, a clot will form that can be dislodged and end up occluding blood flow in the brain or eye. The same can occur when bits of fatty plaque in a carotid artery or disrupted. In the past, there have been case reports like this one (or that one) where this has resulted in visual disturbances.
What makes this case unusual is that it is evidence of the potential for direct traumatic injury to the eye as opposed to the indirect kind of process I’ve just described. The authors of the report have hypothesized that the shearing force of the adjustment tugged on the region where the jelly like filling in your eyeball, known as vitreous, is attached to the retina by millions of tiny fibers. This tugging may have resulted in a small detachment and subsequent bleeding.
Luckily for the patient, they did not find a tear in the retina that would have required surgery and risked permanent vision loss. Her symptoms improved quickly and were completely resolved, as would be expected, by follow-up 2 months later. Unfortunately she was cleared to return to chiropractic care.
I wasn’t able to find a response from the chiropractic community yet, but I have little doubt that it will come.
More fun with case reports?
Here is a list of chiropractic case reports involving the management of blindness and other visual disorders. This is also an interesting read.
Conclusion
Case reports are thin gruel, but they can be interesting and occasionally helpful in the practice of medicine. What they can never be is solid evidence for a causal claim in and of themselves. It requires a thorough understanding of plausibility and pathophysiology, and of the available literature when such a thing exists, to put them into context.
In the case of chiropractic versus the posterior retina, we have to be careful and not give more weight to a report than is deserved just because it is in keeping with our understanding of the risks and benefits of chiropractic. We have to be open to the fact that it is possible that the findings in question happened for some other reason and that the preceding HVLA neck adjustment was a temporal coincidence. That being said, if it looks like a duck, swims like a duck, and quacks like a duck, then it probably isn’t a dugong.