Annular patterns are particularly likely to be found in psoriasis when individual lesions undergo resolution. In such a situation the central portion of a plaque fades, leaving an erythematous border at the periphery. This border is generally wider (5 to 8 mm) than that found in the other annular diseases, and there is a tendency for the border to break up into individual papules. The size of the annular lesions and their configuration depend on the appearance of the plaque that preceded them. Since annularity usually occurs during resolution, centrifugal growth is not commonly seen. Typical psoriatic scale is usually present on the border, but when the disease is under active treatment, the formation of scale is minimal or absent. Diagnosis is not ordinarily difficult, since more typical lesions of psoriasis can be found elsewhere on the body.
Annular lesion’s are found in Microsporum. sp. infections of children and in TrichoPhyton rubrum. infections of adults. In children the lesions are solitary or are few in number. They are usually only 2 to 4 cm in diameter and are generally found on exposed surfaces. Complete circles are formed, and there is relatively little tendency for coalescent growth of adjacent lesions. Scale is always present at the active border. The amount of inflammation and thus the intensity of the redness are highly variable. Potassium hydroxide (KOH) preparations, fungal cultures, or both should be carried out to confirm a clinical diagnosis.
The annular lesions of tinea corporis in adults are quite different. Larger rings are noted, and coalescent growth frequently results in the development of very large lesions with serpiginous borders. Complete circles are not often found, and in fact, gaps in the ring-like border may be large enough to interfere with recognition of the annular pattern. The active, advancing border is quite narrow (1 to 3 mm) and is usually scaling. Postinflammatory hyperpigmentation may be found within the central portion of the lesions as centrifugal growth occurs. New circles can sometimes redevelop in the cleared central area of the larger rings. Tinea corporis in the adult usually begins on the upper, inner thighs and from there extends onto the buttocks and lower trunk around the belt line. Less commonly, the face or dorsal surface of the hands may be involved. The disease is pruritic, and excoriations (fungal eczema) are often present. KOH preparations, fungal cultures, or both should be used to confirm a clinical diagnosis.
The lesions of discoid Lupus Erythematosus (LE) regularly assume an annular configuration when the central portions of otherwise-solid plaques begin to undergo resolution. This resolution often results in the development of hypopigmentation and scarring in the central area. The presence of scarring is a pathognomonic feature of discoid LE. Some of these annular plaques are stable in size, while others show evidence of very slow centrifugal growth. The active border is usually thin, with some evidence of scale formation. Most lesions are 2 to 5 cm in diameter. Lesions are most often found on the face, scalp, and neck, but occasionally the upper trunk and arms are involved. A clinical diagnosis can be confirmed by biopsy.
Annular lesions are also seen in subacute cutaneous LE and, sometimes, in systemic LE. They are located on the trunk and proximal arms rather than on the face and scalp. These lesions greatly resemble those of the gyrate erythemas . On the other hand, they lack the central hypopigmentation and scarring found in discoid-type disease. Pityriasis Hosea. The herald patch of pityriasis rosea regularly demonstrates an annular configuration. The border is brown-red, and fine (pityriasis-type) scale is present. The lesion is usually 3 to 5 cm in diameter and, once present, does not grow in size. The herald patch when seen in the presence of full-blown pityriasis rosea is not difficult to recognize. Unfortunately, when it occurs before the rest of the disease develops, it is easily misdiagnosed as tinea corporis. KOH preparations will, of course, distinguish between the two. The smaller lesions of pityriasis rosea are only rarely annular.
Ringed lesions are sometimes seen in lichen planus, but they are generally outnumbered by more typical flat-topped papules and plaques. Annular lesions when present are quite small, rarely measuring more than 2 or 3 cm in diameter. Both partial and complete circles may be formed. It is sometimes possible to distinguish, within the annulus, individual papules that have not completely coalesced. The color is distinctively violaceous, and the surface is shiny because of the reflective properties of compacted lichenoid scale. Annular lesions are particularly likely to be found on the volar surface of the wrists and on the shaft of the penis. The presence of one or more linear lesions occurring as a result of the Koebner phenomenon is a very helpful diagnostic sign. Biopsy is pathognomonic.
Annular lesions are occasionally seen in secondary syphilis. As in lichen planus, the annular lesions are small, with most being less than 2 cm in diameter. The color is red rather than violaceous. Linear lesions are not found. The annular lesions of secondary syphilis are particularly common on the face and genitalia. Clinical recognition is assisted by the regular presence of other symptoms and signs of secondary syphilis. The serologic test for syphilis will be positive. Biopsy of the lesions is highly distinctive.