If someone is pre diabetic, they would come across certain changes in their health and body. Darkening of knuckles is also one of the primary symptoms.
People with prediabetes can develop a skin disorder called acanthosis nigricans. It shows up as dark, thick patches in areas of your body where there are skin creases or folds. Acanthosis nigricans often appears on the neck, in the armpits, inside the elbows, behind the knees and on the knuckles.
Other key symptoms of diabetes includes increased thirst/hunger, frequent urination, fatigue, blurred vision, nausea, and weight loss/gain.