Squamous Epithelioma possibly Induced by the Therapeutic Application of Tar

THE employment of tar in dermatology has a long history. According to Hebra (1868), Theophrastus, Dioscorides and Pliny advocated its use in the treatment of diseases of the skin. For many centuries this treatment fell into disfavour, partly on account of the general acceptance of Galen's " acrimonia sanguinis " theory ofthe causation ofskin disease which discouraged the use oflocal applications. Hebra gives credit for the re-introduction of tar in dermatology to Bateman and Wilkinson in England, to Rayer, Cazenave and others in France, and to Hertwig, Krieg, Otto and others in Germany and Austria. Until the second half of the nineteenth century only the wood tars were generally available. Contemporary text-books give evidence of their increasing popularity and Pix liquida appeared in the 1867 edition of the British Pharmacopoeia. After the introduction of coal-tar, which was in use for some years before it gained admission to the Pharmacopoeia in 1898, it slowly replaced the wood-tars, but these have not been entirely superseded, and both woodand coal-tars still form an indispensable part of the dermatologists' armamentarium. Tars are employed as anti-pruritics and " reducing agents ". The latter term was coined by Unna and has been defined as " agents which reduce epithelial proliferation, hyperkeratosis and cutaneous infiltrates and normalize faulty keratinisation " (Rothman and Shapiro 1949). Tars are of particular value in the treatment of eczema, lichenification and psoriasis; since these conditions may persist or may recur at frequent intervals for many years it is not unusual for the patient, on medical advice or on his own initiative, to continue for very long periods treatment which provides some symptomatic relief. The coal-tars are in general more often prescribed than the wood and bituminous tars. The official preparations of coal-tar in Britain are: pix carbonis B.P., pix carbonis praeparata B.P., liquor picis carbonis B.P. Pix carbonis is crude commercial coal-tar, a complex mixture of variable composition, containing predominantly the aromatic hydrocarbons, such as benzol, toiuol, naphthalene and anthracene and phenolic substances such as phenol, cresol and various polyhydroxyphenols (Obermeyer and Becker, 1935). By dry distillation four fractions can be distinguished; the light oils (benzol, toluol, xylene and pyridine) medium oils (naphtha, heavy benzene, crude phenol and cresols), and heavy oils (naphthalene, cresols, quinoline, etc.) and the anthracene oils (flourescent green oil, containing acridine and its derivatives). The remainder consists of pitch. Pix carbonis praeparata is commercial coal-tar heated at 500 C. for one hour, in which process certain of the lighter oil fractions are lost. Liquor picis carbonis is made by