Doctors often look for clues on the outside of the body for what might be happening inside. A small study of 191 adults in Bulgaria who were overweight or obese found that a specific skin finding—a horseshoe-shaped patch of thickened skin on the sole of the foot—was more common in those who also had prediabetes. About 25% of people with prediabetes had it, compared to 10% of those without. When present, it was linked to roughly three times higher odds of having prediabetes.
The study involved a dermatologist giving everyone a standardized skin exam. The researchers then compared the 151 participants with prediabetes to the 40 without. They looked for several common skin conditions, but only this particular foot finding, called horseshoe-like plantar hyperkeratosis, showed a significant link. Other issues like dry skin, itching, skin tags, or a yellowish skin tone didn't differ between the groups.
It's crucial to understand what this finding means—and what it doesn't. The skin patch was a specific clue: when doctors saw it, it was a strong hint (90% specific) that prediabetes might be present. However, it was not a sensitive clue, meaning it was absent in most people (75%) who actually had prediabetes. So, missing the patch doesn't rule out the condition. The study design only shows these two things are associated at one point in time; it cannot say if one causes the other. This was also a single-center study, so we don't know if the finding would be the same in other groups of people.
