BLOG: Throw away your microscopes: Cylindrical dandruff is pathognomonic for Demodex
Ewwww! Gross! Have you seen those things?
I mean, even if it was super convenient, quick and easy to pluck an eyelash, cart it over to your microscope and then examine the base of the lash looking for Demodex — even if they paid you to do it — you gotta look at squirming mites that 5 minutes earlier were 8 inches from your face. There must be a better way.
As it turns out, there is.
No matter what problem we are addressing in the clinic, we are always looking for the easiest, most direct and quickest route to making an accurate diagnosis. In doing so, it is better if we can make a diagnosis while doing something that is intrinsic to nearly every exam. As doctors who care for patients suffering from dry eye disease, we examine pretty much every patient we see with a slit lamp. In a perfect clinical world, all we would need to do is our slit lamp exam to gather all of the data we need to choose appropriate therapy.
While it is exceedingly simple to see the signs of meibomian gland dysfunction at the slit lamp, prevailing wisdom has held that making the diagnosis of Demodex as a contributing cause necessitated the above-noted process of plucking an eyelash and hoping to find a mite hanging on for dear life. This is actually an important thing to diagnose. Cheng and colleagues, working in the lab of Dr. Anat Galor at the Miami VA Hospital, found that almost 70% of patients in their clinic who had signs and/or symptoms of DED had Demodex using the pluck and scope strategy.
In the real world, (almost) no one plucks, plods and peers through a microscope to diagnose Demodex. The alternative to plucking eyelashes has been around since 2005. Gao and colleagues set out to determine the prevalence of Demodex in eyelashes with cylindrical dandruff, dandruff that cuffs the base of an eyelash. One hundred percent of subjects with either diffuse or sporadic cylindrical dandruff were found to have Demodex when the epilated lashes were examined vs. 22% of those without this finding. This is a big deal, so let me say that again: Cylindrical dandruff on the eyelash is pathognomonic for Demodex.
Why is this news in 2021? Well, the other conclusion reached by the Gao team was that lid hygiene with shampoo reduces but does not eradicate the mites. Making a diagnosis is only half of the job. Like that famous JFK quote, “It’s not enough to simply be elected, one must be able to govern,” after making a diagnosis, you have to be able to treat the disease. Thankfully, for those of you who don’t have access to intense pulsed light (check out Dr. Laura Periman’s YouTube channel for some seriously creepy video of Demodex mites checking out after IPL), highly effective topical treatments are making their way through the FDA octagon.
For now, I think we should all asking our patients to look down so that we can more easily see the base of the lashes. We should be adding “Demodex” to our diagnoses, especially in a symptomatic DED or MGD patient, so that we are ready to pounce when new treatments arrive.
- Cheng AM, et al. Cornea. 2020;doi:10.1097/ICO.0000000000002542.
- Gao YY, et al. Invest Ophthalmol Vis Sci. 2005;doi:10.1167/iovs.05-0275.