Sаrаh, 21, gоes tо see the dermаtоlogist for recurring itching and redness on her elbows. The dermatologist also notes scaly patches covered by silvery gray scales. With further questioning the dermatologist discovers that Sarah's skin outbreak has occurred periodically for more than 4 years and that her father has had similar periodic outbreaks on his knees and legs for years. The dermatologist diagnoses Sarah's skin disorder as: