What causes pityriasis rosea?

Causes of Pityriasis Rosea

Pityriasis rosea is primarily caused by the endogenous systemic reactivation of human herpesvirus (HHV)-6 and HHV-7. 1, 2

Viral Etiology

• HHV-6 and HHV-7 have been implicated as the primary causative agents in pityriasis rosea 1
• Recent research shows that pityriasis rosea represents a delayed reaction to viral infections, particularly the reactivation of these herpesviruses 3
• The severity of the condition may correlate with viral load - patients with only a herald patch (abortive form) show lower HHV-6/7 DNA plasma loads compared to those with classic widespread eruption 2

Triggering Factors

• COVID-19 infection has been reported to trigger pityriasis rosea, either during acute infection or in the post-COVID period 3
• SARS-CoV-2 may induce reactivation of other viruses like HHV-6 and HHV-7, leading to pityriasis rosea 3
• Certain medications can trigger pityriasis rosea-like eruptions, including:
  • Angiotensin-converting enzyme inhibitors 4
  • Sartans plus hydrochlorothiazide 4
  • Allopurinol 4
  • Nimesulide 4
  • Acetyl salicylic acid 4
• Vaccines have been associated with pityriasis rosea, including those for smallpox, poliomyelitis, influenza, HPV, and COVID-19 3, 4

Host Factors

• Pregnancy is associated with a higher incidence of pityriasis rosea (18% vs. 6% in general population) due to immune changes that favor viral reactivation 4
• Age is a significant factor, with pityriasis rosea occurring mainly in individuals between 10 and 35 years of age, with peak incidence during adolescence 1
• Immune status affects disease presentation - stronger immune responses may result in abortive forms with only the herald patch 2

Clinical Presentation and Diagnosis

• The disease typically begins with a "herald" or "mother" patch in approximately 80% of patients 1
• A generalized bilateral symmetrical eruption develops approximately 4-14 days after the herald patch 1
• Lesions follow skin lines of cleavage (Langer lines), creating characteristic "Christmas tree" pattern on the back 1, 5
• Mild prodromal symptoms (headaches, fever, malaise, fatigue) may occur in about 5% of patients 1

Differential Considerations

• Rosacea is a distinct condition that should not be confused with pityriasis rosea, characterized by:
  • Persistent centrofacial erythema with periodic intensification by trigger factors 6
  • Telangiectasia, inflammatory papules, and pustules 6
  • Association with Demodex mites, which may play a role in its pathogenesis 6, 7
• Demodex infestation is not associated with pityriasis rosea but is commonly found in patients with rosacea and blepharitis 7

Disease Course

• Pityriasis rosea is typically self-limited, lasting 6-8 weeks in most cases 1
• In pregnant women, especially during the first 15 gestational weeks, pityriasis rosea may be associated with increased risk of adverse pregnancy outcomes 4
• Rarely, pityriasis rosea may present as an abortive form with only the herald patch as the sole manifestation 2

Understanding the viral etiology and triggering factors of pityriasis rosea is essential for proper diagnosis and management, particularly in special populations like pregnant women where the condition may have more significant implications.