Leukoderma is as common in housemaids as in field-laborers, and is in no way attributable to exposure of sun or wind. True leukodermic patches show no vascular changes, no infiltration, but a partial obliteration of the rete mucosum. It has been ascribed to syphilis; but syphilitic leukoderma is generally the result of cicatrices following syphilitic ulceration.
Many observers have noticed that negroes become several degrees lighter after syphilization; but no definite relation between syphilis and leukoderma has yet been demonstrated in this race.
Postmortem examinations of leukodermic persons show no change in the suprarenal capsule, a supposed organ of pigmentation.
Climate has no influence. It is seen in the Indians of the Isthmus of Darien, the Hottentots, and the Icelanders. Why the cells of the rete mucosum should have the function in some races of manufacturing or attracting pigment in excess of those of other races, is in itself a mystery. By his experiments on the pigment-cells of a frog Lister has established the relation existing between these elements and innervation, which formerly had been supposititious.
Doubtless a solution of the central control of pigmentation would confirm the best theory of the cause of leukoderma--i.e., faulty innervation of the skin. At present, whether the fault is in the cell proper, the conducting media, or the central center, we are unable to say. It is certainly not due to any vascular disturbances, as the skin shows no vascular changes.
White spots on the nails are quite common, especially on young people. The mechanic cause is the presence of air between the lamellae of the affected parts, but their origin is unknown.
According to Crocker in some cases they can be shown to be a part of trophic changes. Bielschowsky records the case of a man with peripheral neuritis, in whom white spots appeared at the lower part of the finger-nails, grew rapidly, and in three weeks coalesced into a band across each nail a millimeter wide. The toes were not affected. Shoemaker mentions a patient who suffered from relapsing fever and bore an additional band for each relapse. Crocker quotes a case reported by Morison of Baltimore, in which transverse bars of white, alternating with the normal color, appeared without ascertainable cause on the finger-nails of a young lady and remained unchanged.
Giovannini describes a case of canities unguium in a patient of twenty-nine, following an attack of typhoid fever. On examining the hands of this patient the nails showed in their entire extent a white, opaque, almost ivory color. An abnormal quantity of air found in the interior of the nails explains in this particular case their impaired appearance. It is certain that the nails, in order to have admitted such a large quantity of air into their interior must have altered in their intimate structure; and Giovannini suggests that they were subject to an abnormal process of keratinization. Unna describes a similar case, which, however, he calls leukonychia.
Plica polonica, or, as it was known in Cracow--weicselzopf, is a disease peculiar to Poland, or to those of Polish antecedents, characterized by the agglutination, tangling, and anomalous development of the hair, or by an alteration of the nails, which become spongy and blackish. In older days the disease was well known and occupied a prominent place in books on skin-diseases.
Hercules de Saxonia and Thomas Minadous, in 1610, speak of plica as a disease already long known. The greater number of writers fix the date of its appearance in Poland at about the year 1285, under the reign of Lezekle-Noir. Lafontaine stated that in the provinces of Cracow and Sandomir plica formerly attacked the peasantry, beggars, and Jews in the proportion of 1 1/2 in 20;and the nobility and burghers in the proportion of two in 30 or 40. In Warsaw and surrounding districts the disease attacked the first classes in the proportion of one to ten, and in the second classes one to 30. In Lithuania the same proportions were observed as in Warsaw; but the disease has gradually grown rarer and rarer to the present day, although occasional cases are seen even in the United States.
Plica has always been more frequent on the banks of the Vistula and Borysthenes, in damp and marshy situations, than in other parts of Poland. The custom formerly prevailing in Poland of shaving the heads of children, neglect of cleanliness, the heat of the head-dress, and the exposure of the skin to cold seem to favor the production of this disease.