Etretinate therapy stimulates deposition of mucus-like material in epidermis of patients with psoriasis.

During therapy for psoriasis with the oral aromatic retinoid etretinate, a finely granular material was detected by electron microscopic examination of the epidermis of ten patients. Since this amorphous substance has some of the ultrastructural characteristics of mucin, it is called mucus-like material (MLM). MLM occurs occasionally in untreated psoriatic lesions; however, its deposition is enhanced by etretinate therapy. While MLM has not been fully characterized, evidence exists for the possibilities that it represents either cell products (such as mucin, or carbohydrates associated with the cell surface) or an exudate infiltrating the epidermis.