Definition of Pityriasis
Pityriasis refers to a group of skin conditions characterized by scaling of the skin, representing various dermatologic diseases with diverse causations but sharing the common feature of skin scaling. 1
Etymology and Origin
- The term "pityriasis" derives from the Greek word "pityron" meaning "bran" or "scale," referring to the characteristic flaky appearance of affected skin 1
- The term was first documented in medical literature in 1684 according to the Merriam-Webster dictionary 1
Common Types of Pityriasis Conditions
Pityriasis Rubra Pilaris (PRP)
- A rare chronic inflammatory skin condition characterized by follicular papulosquamous eruptions, reddish-orange scaling, palmoplantar keratoderma, and erythema with islands of sparing 2
- Can be classified into 5 types, with type 4 presenting as well-demarcated hyperkeratotic erythematous plaques on elbows and knees with palmoplantar keratoderma 3
- May be mistaken for other conditions like tinea corporis, psoriasis, or atopic dermatitis in early presentations 2, 4
Pityriasis Lichenoides
- A spectrum of skin conditions including pityriasis lichenoides et varioliformis acuta (PLEVA), pityriasis lichenoides chronica (PLC), and febrile ulceronecrotic Mucha-Habermann disease (FUMHD) 5
- PLEVA presents as acute-to-subacute eruptions of small red papules that develop into polymorphic lesions 5
- PLC manifests as small red-to-brown flat maculopapules with mica-like scale and follows a relapsing course 5
- FUMHD is an acute severe form with purpuric and ulceronecrotic plaques and systemic involvement 5
Pityriasis Alba
- A common hypopigmented condition, particularly in children, appearing as pale patches with fine scale 6
- Often considered in the differential diagnosis of vitiligo 6
Pityriasis Rosea
- A self-limiting papulosquamous eruption characterized by a herald patch followed by multiple smaller lesions in a "Christmas tree" distribution pattern 1
Pityriasis Versicolor
- A common fungal infection caused by Malassezia species, presenting as hyperpigmented or hypopigmented macules with fine scale 6
- Included in the differential diagnosis of vitiligo and other depigmenting conditions 6
Clinical Significance
- Pityriasis conditions can be confused with other dermatological disorders, making accurate diagnosis challenging 2
- Some forms, like pityriasis lichenoides, have potential to progress to cutaneous lymphoma or ulceronecrotic presentations with significant mortality risk 5
- Proper diagnosis often requires correlation of clinical features with histopathological findings 2, 4
- Treatment approaches vary widely depending on the specific type of pityriasis 5, 4
Diagnostic Considerations
- Skin biopsy may be necessary for definitive diagnosis, especially in atypical presentations 2
- Repeated biopsies might be required as some forms evolve over time 2
- Wood's lamp examination can be helpful in certain types, such as pityriasis versicolor 6
- Differential diagnosis should include other scaling disorders like psoriasis, eczema, tinea infections, and other papulosquamous disorders 2, 4