The eruption of erythema consists of an uniform redness, with puffiness of the skin, distributed in distinct patches of some size; it is accompanied by little constitutional disturbance. When fever is present, we suspect that the disorder is not erythema, or con clude that the febrile symptoms have some other cause. The skin, though somewhat elevated, has not the hardness of erysi pelas; after the first day or two the color becomes bluish or livid, and this to an inexperienced eye might simulate the dusky red ness of diffuse cellular inflammation ; but the heat and the tension are absent, as well as the constitutional irritation.
One variety only deserves mention on account of its distin guishing characters--erythema nodosum ; most commonly seen on the anterior aspect of the leg, it appears in distinct rounded patches, which are considerably elevated, and very tender.
This variety is believed by some to be a form of rheumatism ; as the attack subsides the patches become soft, and present something very like a sense of fluctuation, but they do not suppurate. In the broadest sense, any red patch on the surface of the body which is not caused by erysipelas might be called erythema. Writers on skin diseases often enumerate all such cases, and describe the various causes which may give rise to the appearance ; it seems better to restrict the name to those instances in which the redness is produced by something more than mere irritation of the skin, and in which it is not sympathetic only, as when a red patch is seen over a joint affected with acute rheumatism. But an erythematous blush so often points out the situation of grave and serious mischief that whenever fever is present it becomes our duty to study the case very carefully, in order to discover the deeper-seated lesion, of which none are more important than cellular inflammation and se condary suppuration.
Urticaria, "nettle-rash," by its very name, gives an idea of its general form; but while the sting of the nettle raises a white wheal on a sensitive skin, the color of the patches of urticaria is generally redder than that of the surrounding surface. This is often perhaps the consequence of its durati6n, just as the mark of a lash is first paler, and then redder than the rest of the skin; sometimes the pat,ches are deep-colored from the first, and when they continue for any length of time, they tend to become purple or bluish. The eruption is attended with tingling or itching ; its
progress is sometimes very rapid, lasting not more than one or two days if it be the result of something taken as food or medi cine; in other instances it continues for a week or two, and oc casionally in its chronic form it may exist in more or less dis tinctness for weeks or months.
It is distinguished from all other cutaneous affections, which are similarly distributed, by its patches being perfectly smooth : there is neither oozing nor desquamation of the surface ; it can hardly be confounded with erythema nodosum, which forms in much larger patches with less defined borders.
I am inclined to regard roseola as a sort of spurious exanthem; it is to be seen when measles are about, as well as when scarlatina prevails, but without the coryza of the one or the sore-throat of the other.
It resembles those diseases in attacking young persons and presenting febrile symptoms, though of a very slight and evanes cent character. It may be best described negatively ; the patches are not small and semilunar as in measles, nor are they punctate and close-set as in scarlatina, and the whole surface is never in volved, as is sometimes the case in the eruptive fevers; though roundish in form, the borders are not defined, nor the surfae,e elevated, as in erythema or urticaria, and there is no attendant irritation or itching.
§ 2. Lichen and Prttrigo.—In this subdivision there is also no necessary breach of surface; the cuticle is elevated in small dis tinct points, without any secretion, and the desquamation is acci dental; the eruption is of the form designated as papular. It seldom happens, however, that it is seen exactly in this condition, because there is always itching, and the top of the papule becomes abraded, leaving a red spot or a small crust of coagulated blood. The diagnosis is not difficult if these circumstances be considered ; and even when, as in the severer form of lichen agrius, suppura tion exists, careful inquiry will disclose that such a condition has only arisen in consequence of the long continuance of the disorder in a c,achectio individual, and was not the form in which it first appeared ; other portions of the eruption may also be discovered in which the papular character is manifest.