Overview
Parapsoriasis is a general term for a group of papulosquamous skin diseases characterized by chronic, asymptomatic and erythematous scaling. They include small plaque parapsoriasis, large plaque parapsoriasis, acute or chronic licheniformis acuta (PLEVA) and pityriasis lichenoides chronic (PLC). These diseases are prone to coexist or overlap with each other and are associated with cutaneous T-cell lymphoma.
(i) Small plaque parapsoriasis and large plaque parapsoriasis
Epidemiology
Small plaque parapsoriasis and large plaque parapsoriasis are most common in middle-aged or elderly people, but can also occur in children. 40-50 years of age is the peak incidence and can occur in all races and regions. Small plaque psoriasis is more common in men, with a male to female ratio of approximately 3:1.
Pathogenesis
The pathogenesis of small plaque parapsoriasis and large plaque parapsoriasis is unknown. Both diseases are characterized by a lymphocytic infiltration of CD4+ T cells in the superficial dermis. It is now generally accepted that small plaque parapsoriasis and large plaque parapsoriasis are fundamentally different diseases, while large plaque parapsoriasis is closely related to the mycosis fungoides plaque phase. Studies have found that large plaque psoriasis has an approximately 10% chance of progressing to cutaneous T-cell lymphoma every 10 years [1].
Clinical features
Both of these diseases have a chronic course and are often asymptomatic or only mildly pruritic. Early in the course, the rash is mild to severe and slowly progressive, and lesions may be widely distributed on the trunk and extremities or confined.
The typical lesions of small plaque type parapsoriasis are round or oval red or reddish-brown patches less than 5 cm in diameter, covered with fine scales. “Finger-shaped dermatitis” is an important clinical type of small plaque parapsoriasis, which presents as long, symmetrically distributed finger-shaped patches on the rib cage, the long axis of the lesions may be larger than 5 cm, and does not usually progress to cutaneous T-cell lymphoma.
Large plaque parapsoriasis presents as round or irregularly shaped red or maroon patches covered with scales, often larger than 5 cm in diameter, and may also present with epidermal atrophy, capillary dilation, and hyperpigmentation or hypopigmentation.
Dermatopathology
Small plaque parapsoriasis presents with mild, nonspecific spongiform edematous dermatitis with keratosis imperfecta. Large plaque parapsoriasis may present with lymphocytic infiltration at the superficial dermal interface with varying degrees of mossy infiltration in the upper dermis. Some macular parapsoriasis is pathologically indistinguishable from mycosis fungoides, and atypical lymphocytes are often seen.
Diagnosis and differential diagnosis
The diagnosis of plaque parapsoriasis often requires a combination of clinical manifestations, disease course and dermatopathological changes. In some cases it is a diagnosis of exclusion. Inflammatory skin diseases that need to be differentiated from plaque psoriasis include pityriasis rosea, drug rash, psoriasis, coin-like eczema, chronic eczema, stage II syphilis rash, and chronic radiation dermatitis. In addition, the establishment of a diagnosis of parapsoriasis must first exclude the possibility of mycosis fungoides.
Treatment
Treatment of plaque parapsoriasis is generally preferred to skin-targeted therapy. These include topical medications such as corticosteroids, topical coal tar preparations, topical nitrogen mustard preparations, topical bezarotene; and ultraviolet phototherapy, including narrow-spectrum UVB and photochemotherapy.
(B) Acute acneiform mossy furunculosis and chronic mossy furunculosis
Epidemiology
Acute and chronic pemphigus vulgaris represent different ends of the pemphigus vulgaris spectrum of disease. Pemphigus vulgaris occurs most often in children, but can be seen in all ages, races and regions, and is more prevalent in males.
Pathogenesis
The etiology of pemphigus foliaceus is unknown and may be related to foreign antigens such as infectious antigens, such as viruses, or drug reactions.
Clinical manifestations
Pityriasis vulgaris presents as an erythematous to pruritic papule that appears in batches and may subside spontaneously, but recurs. The acute form (PLEVA) and the chronic form (PLC) can occur in succession during the course of the disease. The lesions of acute pimple-like mossy furunculosis may develop into crusts, ulcers, blisters, or pustules, and the rash can usually resolve spontaneously after a few weeks, with scarring after healing if the dermis is severely damaged. The lesions are usually confined to the skin. Occasionally, acute lesions may be accompanied by symptoms such as discomfort, fever, and generalized lymph node enlargement. Chronic mossy furunculosis lesions appear as papules, red to maroon, covered with scales. There are usually no conscious symptoms and the lesions fade within weeks to months, leaving behind hypopigmented patches; or they have a chronic course with recurrent attacks [2].
Dermatopathology
All lichen planus furunculosis present as interface dermatitis. In the acute phase, the lesions appear as superficial deep dermal perivasculitis with interfacial dermatitis. There is a wedge-shaped infiltration of intra-dermal lymphocytes with neutrophils. The epidermis is focally hyperkeratotic, often with keratinocyte necrosis and erythrocyte extravasation. Lymphocytic vasculitis is sometimes seen, but mostly without fibrinoid necrosis of the blood vessels. Pathological changes in chronic phase lesions include keratosis imperfecta, mild lymphocytic infiltration at the interface, focal keratinocyte necrosis and mild erythrocyte extravasation [3].
Diagnosis and differential diagnosis
The diagnosis of mossy furunculosis is based on clinical features, combined with histopathological changes of the lesions. Differential diagnoses to be excluded are: lymphomatoid papulosis, cutaneous microvascular vasculitis, drug rash, arthropod bites, chickenpox, folliculitis, erythema multiforme, and herpes-like dermatitis [4].
Treatment
Treatment of pemphigus vulgaris is generally preferred to skin-targeted treatment. This includes topical medications such as corticosteroids, topical coal tar preparations, topical nitrogen mustard preparations, and topical bezarotene; and ultraviolet phototherapy, including narrow-spectrum UVB and photochemotherapy. In patients with more severe systemic symptoms with infection and associated fever and arthritis, systemic therapy may be used, including antibiotics, hormones, or low-dose immunosuppressive agents such as methotrexate.
References
[1] Klemke CD, Dippel E, Dembinski A, Ponitz N, Assaf C, Hummel M, et al. Clonal T cell receptor gamma-chain gene rearrangement by PCR-based GeneScan analysis in the skin and blood of patients with parapsoriasis and early-stage mycosis fungoides. J Pathol. 2002;197:348-54.
[2] Bowers S, Warshaw EM. Pityriasis lichenoides and its subtypes. J Am Acad Dermatol. 2006;55:557-72; quiz 73-6.
[3] Wood GS, Strickler JG, Abel EA, Deneau DG, Warnke RA. Immunohistology of pityriasis lichenoides et varioliformis acuta and pityriasis lichenoides chronica. evidence for their interrelationship with lymphomatoid papulosis. J Am Acad Dermatol. 1987;16:559-70.
[4] Zhu X.J., Wang B.X., Sun J.F., and Xiang L.H., eds. Dermatology January 2011 First Edition; Peking University Medical Press.