Where does a herald patch typically start?

Herald Patch in Pityriasis Rosea: Location and Characteristics

The herald patch in pityriasis rosea typically starts on the trunk, most commonly appearing as a single erythematous plaque before the generalized rash develops. 1, 2

Typical Location and Appearance

• The herald patch most frequently appears on the trunk as the initial manifestation of pityriasis rosea 1, 2
• It presents as an erythematous lesion with an elevated border and depressed center, measuring approximately 2-10 cm in diameter 1
• The patch is typically solitary, appearing as a discrete lesion that seems to arise from a single focal point 1
• After the herald patch appears, the secondary eruption usually follows within 1-2 weeks, with smaller lesions distributed along Langer's lines (cleavage lines of the skin) 1, 2

Distribution Pattern

• Following the herald patch, secondary lesions typically form a characteristic pattern:
  • A "Christmas tree" distribution on the back 3, 2
  • A V-shaped pattern on the upper chest 3
• The secondary eruption follows the lines of cleavage (Langer's lines) on the trunk and proximal extremities 2

Clinical Course

• The herald patch appears first and is followed by the generalized rash approximately two weeks later 1
• The entire condition is self-limiting, with the rash typically resolving within 2-10 weeks without treatment 4
• In rare cases, the herald patch may be the only cutaneous manifestation of pityriasis rosea, representing an abortive form of the disease 5

Atypical Presentations

• While uncommon, multiple herald patches can occur in some cases 3
• Atypical forms of pityriasis rosea exist but generally follow a course similar to the classic form 2
• Erythema multiforme-like lesions can occasionally be seen in atypical presentations 4

Differential Diagnosis

• The herald patch may be confused with tinea corporis (ringworm), secondary syphilis, or erythema annular centrifugum 3, 1
• Other conditions in the differential diagnosis include seborrheic dermatitis, nummular eczema, and drug eruptions 1

Understanding the typical trunk location of the herald patch is crucial for early recognition and diagnosis of pityriasis rosea, helping to differentiate it from other similar-appearing skin conditions.