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Pityriasis lichenoides (PL) is a self-limiting, sporadic disease of unknown origin. Cases are reported worldwide and in patients of all ethnic origins. The pathogenesis of PL is not well understood ; however, CD4+ T helper cells are heavily implicated, and alterations in T-cell function and cytokine production, secondary to TNF inhibition, may be responsible for triggering the disease.
Pityriasis lichenoides is a rare condition, with one case for every 1000 to 1500 new patients and no sex bias. It starts in childhood in 20 percent of cases. Pityriasis lichenoides is generally subdivided into:
– an acute form : parapsoriasis varioliformis, pityriasis lichenoides and varioliformis acuta or Mucha-Haberman disease;
– a chronic form : Juliusberg pityriasis lichenoides or pityriasis lichenoides chronica (PLC).
Some authors distinguish a third hyperacute form called Febrile Ulceronecrotic Mucha-Habermann Disease (FUMHD).
Current findings tend to indicate that this is the case and to provide a solution to the question of whether pityriasis lichenoides and lymphomatoid papulosis are two presentations of the same entity. This is important, given the link between lymphomatoid papulosis and lymphoma. In the English literature, the term pityriasis lichenoides is preferred to avoid confusion with plaque parapsoriasis, which is considered to be the initial stage of mycosis fungoides (MF).
It is important to remember that patients with lymphomatoid papulosis may also experience a process compatible with pityriasis lichenoides before or afterwards. More, recently some cases of PLC evolving into MF have been described, mainly in children.
The acute form is characterised by pink, orange or purpuric papules surrounded by an erythematous halo which can become vesicular, eventually developing into bloody, blackish crusts. The lesions, which may become ulcerated and leave scars, tend to multiply and form a rash. Some patients may also present with a fever and malaise. This form develops over a few weeks to several months. With the chronic form, the lesions are brownish-red papules with a central, sticky crust that tends to slough off spontaneously. These lesions heal without leaving any scars, but cause temporary pigmentation disorders. This form may develop over a number of years. Both forms may be accompanied by mild itching.
Febrile Ulceronecrotic Mucha-Habermann (FUMHD) is an exceptionally rare and severe form of pityriasis lichenoides characterised by systemic signs, including a high temperature (40 to 41°C), neurological signs, asthenia and impaired general state, abdominal pain, interstitial lung disease, lymphocytic myocarditis, rheumatologic manifestations and death. Febrile ulceronecrotic Mucha-Habermann disease has been described in young adults. Bacterial secondary infection of the skin lesions is a possible complication. As both acute and chronic lesions may co-exist in the same patient and as there is no correlation between the severity of the lesions and the duration of the condition, the classification proposed is based on lesion distribution. Generally speaking, the lesions are located mainly on the trunk and at the roots of the limbs, but acral forms have been described ; in some cases, the mucosa may also be affected.
The differential clinical diagnoses include guttate psoriasis, chickenpox, secondary syphilis, pityriasis rosea (Gibert), Gianotti-Crosti syndrome and lymphomatoid papulosis. In patients with psoriasis, the erythema is shiny and the entire lesion has a white scaly covering. Chickenpox occurs in epidemics and generally develops rapidly. Secondary syphilis lesions generally do not have the brown and/or haemorrhagic crust and the disease can be isolated in the serum. Pityriasis rosea can be diagnosed by the presence of the "herald" patch and the typical ring-shaped flaking. The peripheral forms of pityriasis lichenoides can be mistaken for Gianotti-Crosti syndrome or vascular purpura but haemorrhagic lesions are not present in these conditions. Lymphomatoid papulosis can resemble pityriasis lichenoides et varioliformis acuta, but the lesions are smaller and less numerous.
The histological signs of acute pityriasis lichenoides are focal parakeratosis with neutrophils in the flakes, intense spongiosis, abundant necrotic keratinocytes and numerous lymphocytes and extravasated red blood cells in the epidermis. The papillary dermis may contain a superficial lichenoid infiltrate, combined with oedema and red blood cell extravasation. The infiltrate consists of lymphocytes, histiocytes, neutrophils and eosinophils and may also be deep and perivascular. The vacuolisation may result in sub- and intra-epidermal vesicles, potentially causing necrosis of the entire epidermis. When the course of pityriasis lichenoides is less aggressive, the infiltrate is confined to the vessels in the superficial plexus, with no oedema in the papillary dermis and slight extravasation of red blood cells. The vacuolisation and ballooning are not accompanied by vesiculation, and no neutrophils are present in the zones of parakeratosis. However, it is likely that acute and chronic pityriasis lichenoides are two different expressions of the same process.
The etiopathogenesis of pityriasis lichenoides remains unclear. Different infections have been suggested, including brucellosis, toxoplasmosis, staphylococcus, streptococcus, type 11 adenovirus, EBV and HIV. The detection of spirochete particles using Warthin and Starry dye and the identification of the B. burgdorferi genome in lesions resembling those of pityriasis lichenoides using PCR tend to indicate infection by spirochetes. A case of pityriasis lichenoides and varioliformis acuta after ingestion of astemizole has also been described. No specific anomalies were found in the laboratory tests. Immunofluorescence may show IgG and IgM deposits, and the presence of complement in the dermal vessels. Most of the cells in the infiltrate are T lymphocytes : CD8+ outnumber CD4+ cells. Tests for activation or proliferation markers (CD30 and Ki67, respectively) tend to be negative, which is not the case with lymphomatoid papulosis.
INFORMATION FOR PATIENTS
Patients must be informed that pityriasis lichenoides is a harmless, but chronic condition that lasts a few months or years in most cases. They must also be aware that the lesions appear in flares and that most of them will heal without leaving scars, although slight pigmentation disorders are possible. It is also useful to mention that the lesions will be most numerous and severe on the trunk. Even in the unfortunate event of varioliform or leukodermic scars, the marks will tend to be limited to parts of the body that are generally covered and therefore will not have a major impact on appearance.
The itching caused by flares is irritating but not unbearable or of the kind that will disrupt the sufferer’s daily life. It can, in any case, be controlled effectively with drugs. Other symptoms, such as a burning sensation, can appear but these are most often of short duration.
It is important to reassure the patient by stressing that the rash usually affects the skin only and is not life-threatening or contagious. The recommended work-up is intended to ensure that the patient does not present any underlying systemic disorders and to screen for an infection which will then be treated. Any examinations and treatment required may be done in the home or at the out-patient clinic. However, patients with the febrile ulceronecrotic Mucha-Habermann form must be informed about the severity of their disorder and admitted to hospital.
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