Diagnosis: Pityriasis rosea
This patient was given a diagnosis of pityriasis rosea based on the clinical presentation.
Pityriasis rosea is a common erythematous and scaly disease that typically starts as a “herald patch” and later spreads as generalized eruptions on the trunk and extremities (secondary eruptions). The herald patch is a large lesion with an oval or round shape. Secondary lesions always occupy lines of cleavage (Langer’s lines), giving the eruptions a characteristic Christmas tree appearance. Some patients may exhibit significant pruritus. Both the herald patch and secondary eruptions show collarette scales, a hallmark of pityriasis rosea.1-3
A viral cause
The etiology of pityriasis rosea is uncertain and is most likely viral, possibly caused by human herpesvirus (HHV-6, -7, or -8).2,3 However, other viruses may also play a role. Also, the incidence of pityriasis rosea rises during the cold weather months.4,5
Immune dysregulation? Pityriasis rosea may be a presenting feature of immune dysregulation in patients with HIV infection or systemic malignancy. It may also occur with increasing frequency in those receiving chemotherapy or immunosuppressive drugs, pregnant women, and patients with diabetes.2,3
Resolves on its own. Pityriasis rosea is generally self-limiting—without any systemic complications—and resolves within 2 to 8 weeks of the appearance of the initial lesion.
Differential includes dermatophytosis and psoriasis
Pityriasis rosea must be differentiated from dermatophytosis, secondary syphilis, psoriasis, pityriasis lichenoides chronica, erythema annulare centrifugum, and pityriasis rosea-like drug eruptions.1-3,6
Dermatophytosis presents as an annular lesion with central clearing and a peripheral papulovesicular border. Patients will complain that the lesions are itchy. Skin scrapings for potassium hydroxide (KOH) preparation reveal fungus under light microscope. (Lab tests do not aid in the diagnosis of pityriasis rosea.)
Secondary syphilis should be suspected in patients with a history of genital ulcers. Patients will have generalized lymphadenopathy and a dusky erythematous papulosquamous rash that involves the palms, soles, and mucosa. A venereal disease research laboratory test will be positive.