There are three different forms of pityriasis lichenoides, namely, pityriasis lichenoides chronica (PLC), pityriasis lichenoideset varioliformis acuta (PLEVA), and febrile ulceronecrotic Mucha-Habermann disease (FUMHD). It is a relatively uncommon skin condition and while its three forms may occur independently, there is a possibility for one form to develop into another.
Although the disease occurs in people of all races and ages, there is a higher prevalence among males, and it tends to have a peak incidence in late childhood and into early adulthood. Moreover, the spectrum of the disease across its forms ranges from mild chronic (PLC) to acute (PLEVA) to severe acute (FUMHD) and none are contagious.
Pityriasis lichenoides chronica (PLC)
PLC is also known as chronic guttate parapsoriasis and parapsoriasis lichenoides chronica. It is the chronic form of the disease characterized by evolving clusters of erythematous (red), scaly papules that usually persist for months. These lesions may relapse and remit over a period of years. At first, the lesions are small pink papules that turn red-brown. These evolve into a mica-like adherent scales attached to the center of the spots, which then flatten out over a period of many weeks to form brown spots that eventually fade away over time. Unlike the lesions in PLEVA, those of PLC are not irritable, itchy, or painful.
Of the three forms of pityriasis lichenoides, PLC is the most common. The lesions have fine scale peels at their edges and may appear anywhere over the trunk, upper arms, and thighs and rarely affects the face or scalp. They are typically mild and do not form any scars when they heal. Although the cause of pityriasis lichenoides in general is unknown, it has been thought that PLC is caused by a hypersensitivity reaction to drugs such antihistamines and vaccines. In addition, bacterial or viral infectious agents such as Epstein-Barr virus (EBV) and Parvovirus B19 (PVB19) have also been implicated. There is no formal treatment for PLC; however, therapies such as ultraviolet light, steroids, and ointments have all been employed.
Pityriasis lichenoides et varioliformis acuta (PLEVA)
PLEVA is a more severe and less common version of PLC. It is also known as acute guttate parapsoriasis and parapsoriasis lichenoides et varioliformis acuta. The lesions of PLEVA are characterized by red patches that quickly evolve into papules. These lesions may occur singly or may present in groups with the possibility of coalescing to form very large areas of rash. While PLC does not cause itching, PLEVA manifests with a burning and itching sensation and may cause scarring and skin discoloration. Despite their dissimilarity in intensity, PLEVA has a similar distribution on the body like PLC and is also proposed to have infectious triggers such as EBV, PVB19, HIV, and toxoplasmosis. Likewise, the treatment options for PLEVA are fairly similar to those used for PLC.
Febrile ulceronecrotic Mucha-Habermann disease (FUMHD)
FUHMD is the most rare and aggressive of the three forms of pityriasis lichenoides with a reported mortality rate of 20% in adults. FUHMD typically begins as PLEVA, but then very rapidly deteriorates to a condition with large ulcers that are filled with pus and blood that are often responsible for secondary infections. There is usually an accompanying high fever with painful skin tissue loss, and many signs including sore throat, abdominal pain, splenomegaly (enlarged spleen), conjunctival ulcers, and other nonspecific symptoms. Rapid diagnosis and treatment of FUHMD is essential to reduce morbidity and death associated with the disease. Due to increased serum levels of tumor necrosis factor alpha (TNF-a), TNF-a inhibitors have been employed as first line treatment in the fight against FUHMD. According to studies, their effectiveness in treating the condition is still under investigation.