American Board of Psychiatry and Neurology (ABPN) Practice Exam

What is the distinguishing feature of dermatomyositis compared to other myositis conditions?

1. Presence of a characteristic skin rash

2. Involvement of distal muscles

3. Response to immunosuppressive therapy

4. Age of onset

The correct answer is: Presence of a characteristic skin rash

The distinguishing feature of dermatomyositis is the presence of a characteristic skin rash. This rash is often recognized as heliotrope rash, which is a purplish discoloration typically found on the eyelids and cheeks, and may be accompanied by other skin manifestations such as Gottron's papules. The presence of this rash is unique to dermatomyositis and helps differentiate it from other types of myositis, such as polymyositis, which generally does not present with skin changes. In dermatomyositis, the inflammatory process affects both the skin and muscle tissues, while in other myositis conditions, the focus is primarily on muscle inflammation. Therefore, the existence of the rash serves as a critical clinical indicator and is integral to the diagnosis of dermatomyositis specifically. The distinctive nature of the skin involvement is essential in guiding further investigations and treatment strategies, highlighting its role as the hallmark feature of this condition.