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Granuloma annulare is a commonly encountered rash. The etiology of this rash is unknown. There are various clinical presentations, including localized, generalized, subcutaneous, actinic, and perforating forms. The generalized version has been seen in association with diabetes. Most cases spontaneously resolve. Multiple treatment strategies exist.

Clinical Findings: Granuloma annulare is a rash that occurs commonly in children but can be seen in any age group. There is no race predilection, but it is twice as common in females as in males. The localized form of granuloma annulare typically starts insidiously as a small, flesh-colored to slightly yellow papule that expands centrifugally. Once the lesion gets to a certain size, its characteristic appearance becomes evident. Fully formed, the area appears as an annular plaque with minimal to no surface change. The plaque appears to have a raised rim around the edge, and the central portion of the lesion is almost normal in appearance. The peripheral rim is slightly yellow in color. The lesions can be entirely flesh colored. Patients experience minimal symptoms. Slight itching may be present. It is not uncommon to have multiple areas of involvement. The dorsal aspects of the feet and hands are common locations for this rash. Some patients relate that their rash is improved during the summer months. The lesions can range from small papules a few millimeters in diameter to larger plaques a few centimeters in diameter. If only small papules exist, a biopsy is required for diagnosis. The clinical appearance of the larger plaques is so characteristic that the diagnosis can be made clinically.

The generalized version of granuloma annulare consists of numerous widespread papules and small plaques. In most cases, there are no annulare-appearing plaques; the diagnosis is considered clinically, but a biopsy is required to confirm the diagnosis. This form occurs almost exclusively in adults and may be seen in association with diabetes. Patients with a diagnosis of generalized granuloma annulare should be screened for diabetes. The other variants of granuloma annulare are uncommonly encountered. They include the subcutaneous form, the perforating variant, and the actinic variant. The actinic variant may be considered a unique entity, termed annular elastolytic giant cell granuloma. Subcutaneous granuloma annulare manifests as deep- seated nodules within the dermis. A diagnosis is made via biopsy. This variant appears to be more common in children. The perforating variant is the rarest form and is the only variant to exhibit surface change. The areas of involvement develop small erosions. This is reported to occur most commonly on the dorsal surface of the hands.
Pathogenesis: The etiology is unknown. It has been theorized to represent an abnormal immune response to a foreign antigen such as a virus or bacteria. This has not been proven, and many other theories of pathogenesis exist. Ultimately, the collagen within the lesions is disrupted, and the resulting inflammatory response causes the clinical findings.
Histology: The histological findings in biopsy specimens of granuloma annulare are very specific. There are areas of necrobiotic collagen with a surrounding granulomatous infiltrate. The collagen is being destroyed centrally. A varying amount of mucin is present. The main histological differential diagnosis is between granuloma annulare and necrobiosis lipoidica. The inflammation in necrobiosis lipoidica is typically oriented across the entire biopsy specimen in a layered fashion. Histological variants of granuloma annulare exist, including interstitial granuloma annulare.
Treatment: Localized forms of granuloma annulare that are asymptomatic and not causing any distress to the patient can be left alone. Most cases resolve spontaneously over time with no residual scarring and no clinically noticeable abnormality. Topical corticosteroids may be used to try to decrease the inflammatory response. Intralesional corticosteroids can be used in some cases, but the risk of atrophy from the steroid injection must be considered. Generalized forms are not amenable to topical therapy. Phototherapy has been used successfully. Psoralen + ultraviolet A light (PUVA) therapy has had more success than ultraviolet B (UVB) light therapy, most likely because UVA light penetrates deeper into the dermis than UVB. Phototherapy with UVA1 appears promising.