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SynopsisPityriasis rotunda (PR) is a rare cutaneous disorder that may be idiopathic or associated with other medical conditions. It is characterized by one or more scaly, well-defined, round or oval patches or thin plaques, which may be hypo- or hyperpigmented. Of note, most cases have been reported from Japan, Italy, and South Africa.
PR has been classified into two distinct subtypes.
Type 1 occurs predominantly in elderly patients of Asian and African descent and is frequently associated with significant systemic illness such as infection or malignancy, particularly hepatocellular carcinoma or gastric cancer. Lesions are typically hyperpigmented and generally fewer than 40 are present.
Type 2 occurs primarily in patients of Northern European descent younger than 40 years. It has a strong hereditary predisposition. There is no association with systemic illness or malignancy. It is believed by many to exist along a spectrum of congenital ichthyoses. Lesions are typically hypopigmented and more numerous.
L44.8 – Other specified papulosquamous disorders
238639005 – Pityriasis rotunda
Differential Diagnosis & Pitfalls
- Congenital (eg, lamellar ichthyosis, ichthyosis vulgaris) and acquired ichthyoses – Similar histopathologic findings.
- Tinea corporis – Usually annular and can be confirmed by finding fungal hyphae on potassium hydroxide (KOH) preparation.
- Tinea versicolor – May present similarly but can be confirmed by finding fungal forms ("spaghetti and meatballs") on KOH preparation.
- Erythrasma – Will show evidence of bacteria on gram stain as well as coral red on Wood's lamp exam.
- Pityriasis alba
- Pityriasis rosea