Subcorneal pustular dermatitis is a rare chronic skin pathology of unclear etiology, characterized by bullous–pustular rashes. It is clinically manifested by the appearance of erythema, against which small flictenes with acantholytic cells inside and a red border around the perimeter are formed. The elements have clear boundaries and are prone to grouping. They are localized on the trunk and limbs, are opened with the formation of surface erosions and the outcome in hyperpigmentation. The diagnosis is made clinically and histologically, using samples of Tzanka and Yadasson. Treatment includes antibacterial therapy, corticosteroids, retinoids externally and internally, UFOs.
L13.1 Subcorneal pustular dermatitis
Subcorneal pustular dermatitis is one of the rare varieties of pustular psoriasis of unclear genesis, possibly a specific transitional state from vesicular dermatosis to psoriatic pustulosis. The first description of the pathological process was given in 1872 by the Austrian dermatologist F. Coat of arms. Officially, subcorneal pustular dermatitis began to be considered as an independent nosological unit only since 1956, after British dermatologists Sneddon and Wilkinson were able to prove the uniqueness of its clinical manifestations.
The pathological process has no seasonal and racial characteristics, and is not endemic. There is evidence that the disease occurs in mature women 4 times more often than in men. Exacerbations are observed mainly in the summer. The urgency of the problem for modern dermatology is associated with a violation of the quality of life of patients suffering from subcorneal pustular dermatitis, the possibility of transformation into more severe cases of psoriatic pustulosis and the risk of developing a paraneoplastic process.
Triggers of pustulosis are both exogenous factors (infections) and endogenous disorders (immunological, endocrine). The mechanism of development is not fully understood. It is believed that in the case of the immune genesis of the pathological process, changes occur in immune complexes, and tumor necrosis factor (TNF) or cachectin appears in the blood serum, which is produced by macrophages and T-lymphocytes. The main role of this cytokine is to implement a “self-destruction program” (apoptosis) of malignant cells under the influence of oxygen and nitric oxide. In addition, TNF, depending on the concentration, stimulates the process of inflammation, the synthesis of T-helper cells and B-lymphocytes, but in excess provokes sepsis and cachexia, inhibiting the rate of breakdown of fatty acids. Probably, the “transitivity” of subcorneal pustular dermatitis is largely due to this factor.
Biologically active substances that have immunoregulatory properties, formed when the integrity of the cells of the immune system is violated under the influence of exogenous factors (infection) and endogenous causes (immunological disorders), stimulate the formation of immune complexes that produce interleukins, which increase inflammation and proliferation of dermal cells, increase vascular permeability, cause skin hyperthermia. This is how erythema occurs first, and then pustules form due to the predominance of exudative processes in inflammation.
In endocrine disorders, the leading role is assigned to failures not only in protein, but also in other types of metabolism (fat, carbohydrate). Cachectin causes insulin dependence in diabetes mellitus, increasing blood clotting, having a negative effect on the blood supply to the pancreas and partially disrupting its work. According to the same scenario, the functions of the thyroid and parathyroid glands are disrupted. In parallel, TNF stimulates protein metabolism, supplying an excess of “building material” to the dermis. In response, inflammation occurs in the skin, the proliferation of epidermal cells increases, which leads to the appearance of erythema and pustules.
The pathological process begins with rashes on the skin of the trunk or extremities of the primary elements in the form of hyperemic spots, the surface of which is covered with bullae up to 1.5 cm in diameter with cloudy contents and a sluggish tire. Inside the bullae, as a rule, are sterile, but it is possible to detect single acantholytic cells at the beginning of the process and many at the height of the disease. Along the perimeter, the pustules are surrounded by an inflammatory rim, located herpetiform (arcuate), tend to cluster, quickly open, exposing the erosive surface. As a result, a motley picture is formed on the skin: half of the pustules are covered with purulent-hemorrhagic crusts, half are half-covered with the remaining lids of the pustules. After regression, hyperpigmentation remains in place of the pustules, new bullae may occur. Rashes are accompanied by non-intense itching and a slight violation of the general condition of the patient.
Sometimes secondary pyococcal infection joins the erosions up to gangrenous pyoderma. Most often it occurs in the folds of the skin. Mucous membranes are extremely rarely affected. Nikolsky’s symptom is negative. The primary elements, merging, form foci with uneven borders, which begin to resolve from the center. New rashes immediately appear on the freed surface, since the pathological process lasts for months, visually the skin resembles the outlines of continents on a geographical map. A feature of subcorneal pustular dermatitis is incomplete remission, the duration of which can vary from several months to several years.
The diagnosis presents certain difficulties due to the similarity of the symptoms of the disease with a large number of other pathologies. Dermatologists are guided by clinical manifestations and anamnesis, conduct a test of Tscan for acantholytic cells and an iodine test of Yadasson in order to exclude vesicular dermatoses. If necessary, histology data are used (undergrowth bulls, moderate acanthosis, hyperkeratosis, perivascular infiltrates in the papillary layer). A distinctive histological feature of the pathological process is the absence of spongiform pustules and the presence of local inflammation.
During the diagnosis of subcorneal pustular dermatitis, a biochemical blood test with a detailed description of globulin fractions is used, as well as a blood test for TNF (tumor necrosis factor). It is used to assess the level of immunity protection, determine the possibility of transformation into a paraneoplastic process and the presence of systemic pathology. Subcorneal pustular dermatitis is differentiated with During’s dermatitis, Herb’s impetigo, Andrews bacteroid, pemphigus, bullous eczema.
The difficulty of therapy of the pathological process lies in the absence of a special treatment algorithm. Symptomatic therapy is not effective enough and contributes to incomplete remission of the disease. Therefore, the main direction in the treatment of subcorneal pustular dermatitis is the identification of latent concomitant pathology and foci of focal infection with their correction, as well as the treatment of long-term chronic diseases. For this purpose, antibiotic therapy, retinoids, corticosteroids, sulfones and their various combinations are used, depending on the degree of prevalence and severity of the pathological process. Antihistamines, sulfonamides, vitamin therapy are connected.
Despite the fact that subcorneal pustular dermatitis has a benign course in comparison with other varieties of pustular psoriasis, therapy of severe forms of the disease is carried out in stationary conditions. Externally, hormonal ointments, creams containing retinoids, antibiotics, combined aerosols, aniline dyes are used. UFO and PUVA therapy are prescribed. The prognosis is relatively favorable, taking into account incomplete remission and the possibility of transformation into paraneoplastic processes.