Most cases are idiopathic, but PR has been associated with:
- Malignancy: multiple myeloma, acute myeloid leukemia, prostate adenocarcinoma, gastric carcinoma
- Infection: leprosy, tuberculosis, osteitis
- Autoimmune disease: scleroderma
- Systemic illness: diabetes mellitus, kidney disease, liver disease, heart disease, chronic obstructive pulmonary disease (COPD), hyperprolactinemia
- Other: glucose-6-phosphate dehydrogenase (G6PD) deficiency, malnutrition
Type 1:
- Typically hyperpigmented
- Typically fewer than 30 lesions
- Predominantly in older Asian or Black adults
- 30% of cases associated with systemic illness
- Typically hypopigmented
- Typically numerous (30 or more) lesions
- Primarily in younger patients of Northern European descent
- Strong hereditary predisposition; believed by many to exist along a spectrum of congenital ichthyoses
- Typically no association with systemic illness or malignancy