Seborrheic dermatitis is one of the most frequent dermatosis in the world population (between 2 and 5%). It is characterized by erythematous lesions (inflamed and reddened lesions) well defined, covered by greasy-looking scales, which are located in the areas of highest density in sebaceous glands, such as the scalp, face and upper third of the trunk. This disease follows a chronic evolution, with frequent exacerbations and remissions. It affects men more than women. Its incidence according to age follows a bimodal curve; Seborrheic dermatitis in children is usually limited to the first 3 months of life and the form of adolescence and adulthood reaches a peak incidence between 18 and 40 years, with few cases in advanced ages.
The prevalence of seborrheic dermatitis in tropical countries is higher than in the Nordic countries.
It is currently considered that the origin of seborrheic dermatitis is multifactorial. The following are identified as essential pathogenic factors:
It is a requirement that the lesions are located in the areas of skin where the sebaceous glands are more numerous. Infantile seborrheic dermatitis is closely related to the production of sebum. The activity and size of the sebaceous glands in newborns are conditioned by the action of maternal androgens; however, in the adult, this relationship does not exist, since the rate of fat production is normal. However, this condition is more frequent in Parkinson’s patients, a process that is associated with seborrhea, and it has been shown that treatment with levodopa reduces the excretion of sebum and seborrheic dermatitis improves. The improvement of this disease has also been proven with Isotretinoin, a retinoid that acts in the reduction of sebaceous secretion.
Currently, most authors defend the primary pathogenic role of the lipophilic yeast Malassezia furfur in seborrheic dermatitis. Several physicians report having found a direct relationship between the intensity of seborrheic dermatitis and the density of Malassezia furfur in the affected areas and there are multiple therapeutic trials with antifungal agents (ketoconazole) that have demonstrated the beneficial effect of this drug, which undoubtedly evidence the primary role of this fungus in the pathogenesis of the disease.
The individual immunological reaction to the fungus Malassezia furfur has become the most important factor for the development of the disease. The presence and number of Malassezia furfur are fundamental for the development of seborrheic dermatitis, but only in those individuals who are immunologically susceptible. This predisposition could be genetically conditioned.
There are other factors that, although not considered in the pathogenesis of the disease, contribute to the development or exacerbation of seborrheic dermatitis. These are:
Stress and depressive states are aggravating factors to be taken into account and that patients when questioned relate it clearly.
The high incidence of seborrheic dermatitis associated with neurological disorders such as Parkinson’s disease, facial paralysis, unilateral damage of the Gasser ganglion, syringomyelia, as well as drug-induced seborrheic dermatitis by neuroleptics such as haloperidol and chlorpromazine, has led to a neurogenic theory for the development of this disease. However, no neurotransmitters have been found, nor has the regulation of sebaceous glands of the nervous type been demonstrated.
The incidence of seborrheic dermatitis seems to be higher in tropical countries. Moisture, sweating and alkalinization of the skin are possibly exacerbating factors. The illness tends to get worse during the fall and winter.
The deficit of zinc, essential amino acids and fatty acids can cause seborrheic dermatitis. Alterations of surface lipids have been found in children with seborrheic infantile dermatitis, which indicate an immaturity of the enzyme delta 6-disaturase that regulates the synthesis of linoleic acid to gamma linoleic acid. It is reported a worsening of this disease with the ingestion of alcohol.
For its study, seborrheic dermatitis is divided into 2 clinical forms according to the age of onset:
It appears in the first months of life as an inflammatory dermatosis that is usually located in the scalp, face, diaper areas and flexures. Scalp involvement may be the only manifestation. It begins with erythematous maculae that grow and converge, with very limited borders that are covered with yellow-brown scales, oily, adherent, located preferably in the frontoparietal region. Classically, this form is called a milk crust. The process can be extended and take the retro earplugs and neck. External otitis may present as a complication of the disease. Its onset is also frequent in the diaper area; in this area it appears as erythematous plaques, with a coppery tone and well-defined edges. Erythema affects both the convex areas and the folds. Sometimes it can take a psoriasis like aspect with whitish scales. The pathogenesis has not been elucidated. It is possible that there is an increased production of sebaceous glands, due to maternal and endogenous androgenic stimulation in the first weeks of life. The presence of Malassezia furfur in the skin of children affected by seborrheic dermatitis is significantly. Some authors consider that the pathogenic role of this fungus is evident in childhood seborrheic dermatitis, supported by the fact that the clinical and mycological response is excellent after the administration of ketoconazole.
It is characterized by the presence of erythematous, desquamative lesions that begin in the follicle and peri follicular, which are extended to form well-defined plates, sometimes with the borders circinados. The desquamation, more or less evident, is greasy. The lesions are distributed in the areas with the highest density of sebaceous glands and adopt clinical variations according to their location. In the facial region the genital naso-sulcus, the eyebrows, the interciliar region are especially affected, giving the typical facial clinical picture. The scalp is where adult seborrheic dermatitis is most frequently located, with a prevalence of up to 80% of patients. The milder forms that only present a slight peeling, without erythema, practically all the population has suffered at one time or another of his life. This clinical form is called pityriasis simplex. In more advanced stages, erythematous base lesions can be observed, with the presence of oily, adherent scales, larger than in the previous clinical form, accompanied by pruritus, which is the so-called steatoid seborrheic dermatitis. In the most intense cases the cluster of whitish scales of the color of the asbestos arrives to cause the formation of plaques that agglutinate the hairs, it is the so-called asciaceous form of the seborrheic dermatitis. Sometimes the seborrheic dermatitis acquires a psoriasis like aspect due to the presence of plaques hyperkeratotic, with furfuraceous desquamation that exceeds the hairline in pre and retro auricular areas and the back of the neck, which make differential diagnosis histologically with psoriasis of the scalp. The involvement of the auditory canal, and sometimes of the flag shell is common in elderly women and is characterized by erythematoscamous lesions, dry scales and little adherence, located in the external auditory canal. Pruritus and secondary infection are frequent, and sometimes lead to external otitis l and even erysipelas. Seborrheic blepharitis can occur in isolation as the only manifestation or accompany other manifestations of seborrheic dermatitis in different typical locations. It is clinically characterized by erythema and adherent desquamation at the base of the eyelashes, especially the upper eyelid. A meibomitis can complicate the picture by the occlusion of these glands with the formation of very painful small abscesses. In the involvement of the thoracic center, more frequent in men, seborrheic dermatitis can acquire 3 clinical forms:
It appears more frequently in women between 25 and 36 years old. Some authors consider this clinical form as a type of seborrheic dermatitis and others as an independent entity. In the most severe cases we can find lesions that affect the folds (armpits, sub mammary areas); clinically, they appear as a well-defined intertrigo, with desquamation of greasy appearance. Bacterial and fungal superinfection is frequent and leads to clinical pictures that are difficult to diagnose.
The genital area can be affected relatively frequently, especially the pubis, where it can show varied clinical morphology, often being confused with other diseases.
The treatment of seborrheic dermatitis will depend on the age of the patient, the location and extent of the lesions, as well as the degree of desquamation and erythema. Before starting treatment it is important to explain to the patient or relatives the chronic but benign nature of the disease, and that the therapeutic measures are aimed at controlling the outbreak.
Drugs used in the treatment of Seborrheic Dermatitis.
We will review the most useful drugs for the treatment of seborrheic dermatitis. These can be grouped according to their mode of action in:
They are used to facilitate the detachment of the scales by solubilizing the cementum and intercellular substances of the stratum corneum. The most commonly used are salicylic acid, urea, retinoic acid, alpha-hydroxy acids, benzoyl peroxide, which has, in addition to keratolytic properties, anti-inflammatory action and certain anti-fungal power against Malassezia furfur. Form of lotions, shampoos, oils or creams, depending on the area to be treated. Selenium sulfide shampoo between 1 and 2.5% and zinc peritiene shampoo, at concentrations between 1-2%, are widely used; both are considered as keratolytic agents; it has been shown that these substances also have a clear fungicidal action against Malassezia furfur. Another frequently used substance is the colander; it is attributed to keratoplastic, antimitotic, antiseptic and anti-inflammatory action. It comes in the form of lotions, creams or shampoos. Recently a liposome co-lighter compound has been commercialized, which seems to be safer and its irritant side effects are minor.
Steroid anti-inflammatory drugs have been used since the 1950s, because they are considered first-line drugs for the control of acute outbreaks of the disease, either alone or in combination with antifungal agents. It is recommended to use low and medium power. The corticoid most used by dermatologists, especially for the treatment of seborrheic facial and infant dermatitis, is hydrocortisone. Recently new medium-potency corticosteroids have been incorporated with few adverse effects, with greater tolerability and anti-inflammatory power, such as prednicarbamate, mometasone furoate and methylprednisolone aceponate. At present, most dermatologists usually treat seborrheic dermatitis by associating an antifungal agent with a corticosteroid.
Since the pathogenic role of Malassezia furfur in seborrheic dermatitis has been demonstrated, antifungals are the first-line treatment. Ketoconazole has been shown to be effective both orally and topically. Topical ketoconazole, in addition to its antifungal action, has some anti-inflammatory action by acting on the erythema and hyperkeratosis present in the lesions. The optimal concentration of topical ketoconazole is 2%. It is indicated in the form of a shampoo for seborrheic dermatitis of the scalp. It should be applied twice a week in acute outbreaks and maintain the treatment for 4 weeks. The cream of ketoconazole 2% is used in the treatment of seborrheic dermatitis of the hairless areas. Oral treatment with this drug is not indicated, due to the possibility of side effects in prolonged treatments, especially at the level of the liver.
Other therapeutic alternatives are the following:
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