Pityriasis rotunda (PR) is an idiopathic, chronic dermatosis that features characteristic discrete, round, scaly, pigmented patches. [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] Pityriasis rotunda may be associated with systemic diseases (eg, hepatocellular carcinoma) in certain racially predisposed groups.
The pathophysiology of pityriasis rotunda is unknown. It may be a variant of ichthyosis vulgaris.
Pityriasis rotunda is a well-known condition in South Africa, Japan, and Italy. Pityriasis rotunda was seen in 65 (1.01%) of 6388 South African medical inpatients. Japanese investigators reported 181 cases of pityriasis rotunda in 1960. Forty-two cases, all from the Italian island of Sardinia, were reviewed in 1997.  In 1989, one review of the English-language literature discussed 89 previously reported pityriasis rotunda patients. Cases of pityriasis rotunda have been reported in Israel, England, Egypt, Portugal, Tanzania, and India. [2, 17, 18, 19, 20, 21, 22]
Most cases of pityriasis rotunda from South Africa, and all 6 cases from America, have occurred in blacks.
In the 1960 review of 181 cases in the French-language literature (performed by Japanese investigators), 175 patients were from Japan, 4 were from Korea, and 2 were from Manchuria. 
Cases have been reported among West Indians living in England. 
No sex predilection has been demonstrated in several large series. One series had 77 males and 63 females; another had 73 males and 101 females. The report of Sardinian patients had 22 males and 20 females. 
Lesions are often first noted in adulthood, usually when aged 20-45 years, but a patient as old as 76 years has been reported. In the review of 42 cases from Sardinia, the average age of onset was estimated to be 3-7 years.
The prognosis for pityriasis rotunda is excellent. Pityriasis rotunda lesions sometimes resolve with treatment of the associated systemic disorder. Lesions of pityriasis rotunda are not associated with mortality, and most are asymptomatic. Pityriasis rotunda can occur with serious underlying systemic diseases, such as hepatocellular carcinoma. [25, 26]