Diabetic dermopathy (also known as "shin spots") is a type of skin lesion usually seen in people with diabetes mellitus. It is characterized by dull-red papules that progress to well-circumscribed, small, round, atrophic hyperpigmented skin lesions usually on the shins. It is the most common of several diabetic skin conditions, being found in up to 30% of diabetics. Similar lesions can occasionally be found in non-diabetics usually following trauma or injury to the area; however, >4 lesions strongly suggests diabetes.
Diabetic dermopathy Wikipedia
The cause is unknown but is thought to be associated with diabetic neuropathy and vascular complications; because the lesions are more common on the shins, some suggest it represents an altered response to injury. It is seen more commonly in patients with longstanding diabetes and poor glucose control.