It may be possible to inquire further and note the effects of lesions, such as the pigment stains remaining after syphilis, lichen ruber and acne; the disfiguring scars of scrofuloderma and lupus vulgaris; the smooth, delicate cicatrices of superficial syphilitic ulcerations. Care must be taken to differentiate lesions natural to the morbid process and those which result from external influences such as crusts, excoriations and wheals from scratching, or from changes brought about by soothing, stimulating, destructive or surgical treatment. Again, it should be remembered that two or more diseases may coexist, and one of them may more or less completely mask the others; thus eczema may be engrafted on a lupus erythematosus, syphilitic ulceration disguised as lupus vulgaris; scabies complicate a psoriasis; or impetigo change the appearance of a varicella. Certain lesions are pathognomonic whenever found in association with other signs of a disease. Such are the sulphur-yellow cups of favus; the broken stubble hairs of tinea capitis; the burrows of the itch mite; the ova on the hairy parts, and the hemorrhagic points on the non-hairy parts, in pediculosis; the flat, glistening papules in lichen planus; and the apple-jelly nodules of lupus vulgaris.

The evolution of a lesion may assist in differentiating it from similar lesions. Lesions may spread by peripheral extension and, at the same time, clear in the center as seen in ringworm of the body and some types of erythema multiforme, or without tendency to clear centrally, as in dermatitis seborrhoica. When adjacent rings expand to meet each other, the sections in contact disappear but the free border continues to extend, forming irregular curves and figures as in some cases of psoriasis.

The distribution and extent of lesions may be characteristic. Symmetrical arrangement of lesions is usually due to constitutional influences or to the presence in the circulation of irritants or poisons. The lesions of the exanthemata and those from the ingestion of the iodine salts are examples of this feature. Unsymmetrical distribution of lesions is largely due to agents primarily acting upon a local part as the local infection of lupus vulgaris, or through the nerves of a part as in zoster. Universal and generalized distributions, may be noted as specified below. The lesions of some skin diseases commonly begin in certain regions; for instance, dermatitis seborrhoica upon the scalp, psoriasis upon the extensor aspect of the elbows and knees and thence by preference to the other extensor surfaces. The following table, showing the tendency of cutaneous diseases to develop in certain regions of the body surface, is included because it is most helpful in diagnostic procedure.

Frederick Dearborn
Dr Frederick Myers DEARBORN (1876-1960)
American homeopath, he directed several hospitals in New York.
Professor of dermatology.
Served as Lieut. Colonel during the 1st World War.
See his book online: American homeopathy in the world war