This is also known as papular acrodermatitis.
It often occurs in association with a viral infection (commonly EBV, enterovirus, echovirus, RSV).
The rash presents as a papular eruption commonly on the extensor surfaces (knees and elbows) but can be found on the buttocks and face. The lesions are usually a dark red colour initially but can become purple and occasionally form into blisters. It can be itchy but often is not.
The rash can last for up to 8 weeks and is commonly associated with lymphadenopathy.
No treatment is required although a topical steroid or emollient can be considered if it is itchy.