The disease is of universal distribution, but is naturally more noticeable in the dark-skinned races. It is much more common in this country among the negroes than is generally supposed.
The "leopard-boy of Africa," so extensively advertised by dime museums over the country, was a well-defined case of leukoderma in a young mulatto, a fitting parallel for the case of ichthyosis styled the "alligator-boy."
Figure 293 represents a family of three children, all the subjects of leukoderma. Leukoderma is more common among females. It is rarely seen in children, being particularly a disease of middle age. Bissell reports a case in an Indian ninety years of age, subsequent to an attack of rheumatism thirty years previous. It is of varying duration, nearly every case giving a different length of time. It may be associated with most any disease, and is directly attributable to none. In a number of cases collected rheumatism has been a marked feature. It has been noticed following typhoid fever and pregnancy.
In white persons there are spots or blotches of pale, lustreless appearance either irregular or symmetric, scattered over the body. In the negro and other dark-skinned races a mottled appearance is seen. If the process goes to completion, the whole surface changes to white. The hair, though rarely affected, may present a mottled appearance. There seems to be no constitutional disturbances, no radical change in the skin, no pain—in fact, no disturbance worthy of note. The eye is not affected; but in a negro the sclerotic generally appears muddy.
It appears first in small spots, either on the lips, nose, eyelids, soles, palms, or forehead, and increases peripherally—the several spots fusing together. The skin is peculiarly thin and easily irritated. Exposure to the sun readily blisters it, and after the slightest abrasion it bleeds freely. Several cases have been reported in which the specific gravity of the urine was extremely high, due to an excess of urea. Wood calls attention to the wave-like course of leukoderma, receding on one side, increasing on the other. The fading is gradual, and the margins may be abrupt or diffuse. The mucous membranes are rosy. The functions of the swell-glands are unimpaired.
The theory of the absence of pigment causing a loss of the olfactory sense, spoken of by Wallace, is not borne out by several observations of Wood and others. Wilson says: "Leukasma is a neurosis, the result of weakened innervation of the skin, the cause being commonly referable to the organs of assimilation or reproduction." It is not a dermatitis, as a dermatitis usually causes deposition of pigment. The rays of the sun bronze the skin; mustard, cantharides, and many like irritants cause a dermatitis, which is accompanied by a deposition of pigment. 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.