Differential diagnosis: Oil drop sign in Psoriasis and Psoriatic Arthritis (PsA)
My colleague and mentor during my first year as a physiotherapist, Martin Thomas, always talked about how there are many things you can glean from assessing the hands and feet from finger clubbing to nail changes.
Up to 80% of patients with Psoriatic Arthritis (PsA), a type of inflammatory arthritis, have nail involvement thus an assessment of a patients’ nails can aid in the clinical reasoning process. Nail involvement is also thought to be a predictor of joint disease and nail changes such as pitting is part of the Psoriasis Epidemiology Screening Tool (PEST).
Recently I saw a patient who had psoriasis and having checked her hands, I noted she had oil drop on two of her nails. Below is brief information around oil drop
The oil drop sign is suggested to be pathognomonic (which means a specific characteristic of a disease or condition) of psoriasis (Sobolowski, 2017).
Without going into too much detail (as this goes way over my head and beyond the scope my reading), oil drop is a problem with compact parakeratosis within the nail bed. As suggested in the diagram below, it seems the difference is that there is nuclei presented the the most superficial part of the skin.
This presents itself on the skin as a discolouration under the nail similar to that of a drop of oil. Below is some photos I have managed to find from some journals.
Hopefully this has given you a snap shot into oil drop and may have spark your interest in nails assessment.
On a final note, through my research on what nail changes look like, I have predominantly found photos of white skin. This lack of diversity of skin colours used in medical research and teaching seems to be a big problem and one highlighted by Malone Mukwende, a medical student at St. George’s University. He has created a fantastic resource called “Mind the Gap: A handbook of clinical signs in Black and Brown skin” to highlight and bridge this gap. It doesn’t have any photos of oil drop as of yet but it is a great resource to use and follow for future updates.
As always, if anyone has any comments, further reading or suggestions on this topic please feel free to fire them at me on here or on my Twitter. I am always learning and any discrepancies on what I have written is thoroughly encouraged.