[Skin changes, pathophysiology and therapy in deficiency of essential fatty acids]

Linoleic acid (C18: 2n-6) is a free fatty acid considered as essential in man; this is mainly based on the fact that man is incapable of its synthesis and that its deficiency accounts for a defined clinical picture. Linoleic acid (LA) is an essential component of cellular membranes and plays, therefore, an important role in cells; moreover, it plays a functional part on account of its precursory position of eicosanoids. For these reasons, the skin is a preferential target in case of LA deficiency, which alters the barrier function of the skin as well as the immunoregulation of the epidermic homeostasis. Man's requirement of LA has been estimated 4% of the total energy supply, i.e. 7-10 g daily. Deficiency of LA may arise from various factors: insufficient supply; metabolic anomalies (mostly due to advanced age and hepatopathies which may particularly alter the metabolic process of desaturation). Symptoms due to LA deficiency are xerosis and erythematosquamous dermatitis. The clinical picture being non-specific may be confused with other vitamin deficiencies, all the more because of metabolic interactions between these vitamins and various trace elements. Thus--in order to make the diagnosis--plasmatic fatty acid fractioning by means of gaseous phase chromatography is indicated in case of therapy-resistant eczematous dermatitis associated with malnutrition. These findings may be confirmed by measuring either the ratio of eicosatrienoic acid vs. arachidonic acid or the ratio of LA vs. arachidonic acid (in case of a disturbed metabolism of fatty acids). The treatment consists of regular oral, parenteral or topical application of essential fatty acids. Topical administration is especially indicated, because these patients, although often suffering from impaired intestinal absorption, reveal a tenfold percutaneous absorption rate of fatty acids.