What is pityriasis rosea?

What is Pityriasis Rosea

Pityriasis rosea is a common, acute, self-limited papulosquamous skin eruption that primarily affects children and young adults, characterized by a "herald patch" followed by oval erythematous scaly lesions distributed along skin cleavage lines in a "Christmas tree" pattern on the trunk. 1

Pathophysiology

• The disease is associated with endogenous systemic reactivation of human herpesvirus (HHV)-6 and/or HHV-7, though the exact causative mechanism remains incompletely understood 2, 3
• Recent evidence suggests SARS-CoV-2 infection may trigger pityriasis rosea, either directly or indirectly through reactivation of HHV-6 or HHV-7 4
• Drug-induced pityriasis rosea-like eruptions can occur with medications including ACE inhibitors, sartans, allopurinol, and imatinib, though these tend to occur at older ages and have shorter duration than classic disease 5, 4

Clinical Presentation

Initial Lesion

• Approximately 80% of patients develop a "herald patch" or "mother patch" - a single, larger erythematous plaque that precedes the generalized eruption by 4 to 14 days 1, 3
• In rare cases (as few as 19 documented patients), the herald patch may be the only cutaneous manifestation, representing an abortive form with lower viral DNA load and shorter duration 2

Secondary Eruption

• The generalized eruption develops in crops over 12 to 21 days following the herald patch 1
• Typical lesions are 0.5 to 1 cm oval or elliptical, dull pink or salmon-colored macules with a delicate collarette of peripheral scales 1
• Lesions are distributed bilaterally and symmetrically on the trunk and proximal extremities 1
• The long axes orient along Langer's lines of cleavage, creating a "Christmas tree" pattern on the back and V-shaped pattern on the upper chest 1, 3

Associated Symptoms

• Approximately 5% of patients experience a mild prodrome including headaches, fever, malaise, fatigue, anorexia, sore throat, enlarged lymph nodes, and arthralgia 1
• Mild pruritus may accompany the eruption 4
• Oropharyngeal lesions occur in approximately 16% of patients with typical pityriasis rosea 4

Natural History and Duration

• The typical course lasts 6 to 8 weeks, though duration may vary from 2 weeks to a few months 1, 3
• The disease is self-limited and resolves spontaneously without treatment in the vast majority of cases 1
• Peak incidence occurs between ages 10 and 35 years, with highest frequency during adolescence 1

Diagnostic Considerations

Key Pitfalls

• Pityriasis rosea in the absence of the herald patch and its clinical variants may pose significant diagnostic challenges 1
• Multiple conditions can mimic pityriasis rosea, including secondary syphilis, drug eruptions, tinea corporis, nummular eczema, and psoriasis 1
• Drug-induced pityriasis rosea-like eruptions can be distinguished histopathologically by the presence of necrotic keratinocytes, interface dermatitis, and eosinophils - features not seen in classic pityriasis rosea 5

Differential Diagnosis Context

• While pityriasis rosea can resemble other erythematous conditions, it should not be confused with erythrodermic psoriasis, pityriasis rubra pilaris, or cutaneous T-cell lymphoma, which are mentioned in the context of severe psoriatic flares but represent distinct entities 6

Management Approach

• In the vast majority of cases, reassurance and symptomatic treatment suffice 1
• Active intervention may be considered for individuals with severe or recurrent disease and pregnant women 1
• When active treatment is needed, oral acyclovir has evidence supporting its use to shorten illness duration 1
• Other treatment options include macrolides (particularly erythromycin) and ultraviolet phototherapy 1
• Topical corticosteroids (such as betamethasone dipropionate) can be used for symptomatic relief and may lead to complete resolution within two weeks 4