Are there any specific investigations required to confirm a diagnosis of pityriasis rosea in atypical cases?

Specific investigations to confirm a diagnosis of pityriasis rosea in atypical cases may include a skin biopsy. This is recommended when the clinical presentation is uncertain or atypical, as biopsy can help confirm the diagnosis histologically ¹.

Routine laboratory tests are generally not required for typical cases, but in atypical presentations, especially if the rash is extensive, persistent, or severe, referral to dermatology for further assessment including biopsy is advised ¹.

There is no standard blood test or microbiological test to confirm pityriasis rosea, as it is primarily a clinical diagnosis. However, atypical variants and differential diagnoses may necessitate exclusion of other conditions through targeted investigations ¹.

Recent literature supports the use of biopsy in atypical or unclear cases to differentiate pityriasis rosea from other dermatoses, emphasizing its role in confirming diagnosis when clinical features are not classic (Chuh et al., 2005; Urbina et al., 2017).