An eruption of yellow-red papules on the trunk, arms, and legs of an adult

A 68-year-old Caucasian man presented with a 6-month history of firm skin papules, starting on his face then gradually moving caudally, progressing to his arms, trunk, and legs (Figure 1). Many of his lesions were asymptomatic. However, a few of the papules were pruritic. The itching was alleviated by topical steroids. On physical exam, multiple yellow-brown to red firm papules and small nodules were noted on the face, trunk, and proximal extremities. Dermoscopic examination demonstrated orange-yellow color surrounded by an erythematous border with occasional linear branched vessels (Figure 2). Histopathologic evaluation of 4 of the lesions revealed spindle cells in the upper dermis (Figure 3). All 4 specimens had similar findings. Immunohistochemical studies showed positivity for CD163, as well as Factor XIIIa. There was no significant positivity for CD34. Laboratory data revealed a hemoglobin A1C of 9.3% and triglycerides of 461 mg/dL. An ophthalmology consult was obtained and no ocular pathology was found. A serum protein electrophoresis was negative. With this information, a diagnosis of adult eruptive xanthogranulomas was made.

An ophthalmology consult was obtained and no ocular pathology was found. A serum protein electrophoresis was negative. With this information, a diagnosis of adult eruptive xanthogranulomas was made.

Discussion
A xanthogranuloma (XG) is a type of non-Langerhans cell histiocytosis that most commonly presents in infancy and childhood; however, several cases have been described in adults. Xanthogranulomas present as dome-shaped papules or nodules on the skin. The condition typically presents with a solitary yellow to reddish-brown growth. However, several cases have been described of eruptive XGs in adults, or adult xanthogranulomas (AXGs) [1][2][3]. The differential diagnosis of XGs is extensive and is based on clinical appearance, associated comorbidities, histology, and immunohistochemistry.
Given the patient's elevated Hg A1C, eruptive xanthomas (EXs) were considered. In addition to diabetes mellitus, EXs    also have clouds of pale yellow dispersed through the papule ( Figure 1). In one study, 90.9% of confirmed XGs had this "setting sun" finding [5]. If suspicion is still high for a BCC, look for other findings of BCC such as leaf-like structures, blue-gray ovoid nests or globules, spoke-wheel structures, shiny white areas, or ulceration.

Conclusions
Our case represents the somewhat rare diagnosis of AXG. The diagnosis was suspected based on dermoscopy and clinical morphology and was confirmed by histopathology (and laboratory ruled out other, similar diagnoses). XGs will usually resolve in children, while only approximately half of adult XGs regress [1]. Our patient was treated with shave removal of symptomatic XGs with good results; however, isotretinoin can also be used, with possible recurrence of lesions with discontinuation. Currently, the etiology of AXG in otherwise healthy adults is unclear. Dermoscopy can help with diagnosis and will show a characteristic yellow-orange hue, called the "setting sun" sign, and is sometimes accompanied by linear, branched vessels around the border (Figure 4). This can be reassuring to both patients and physicians to help rule out skin carcinoma in which the color is not yellow and vessels tend to arborize across the lesion. Finally, while most cases of adult eruptive XGs are idiopathic, reports have linked them with hematologic and rarely solid organ malignancy; therefore, close monitoring of patients with eruptive AXGs is warranted [6].
extremities, in addition to his face. Histopathology was also not consistent with NXG. Finally, NXG can have ocular involvement, which we ruled out with an ophthalmologic examination. PNH was thought to be a less likely diagnosis, given the clinical features that are usually seen with this disease, such as facies leonina, and its progressive nature. Our patient has normal facies and to date has not experienced progression of the disease, but will continue to be monitored.
Finally, generalized eruptive histiocytosis was also on the differential as a type of symmetric papular eruption of the skin on the trunk and proximal extremities. However, this diagnosis was less likely given the histopathologic findings.
Our patient had multiple foamy spindle-shaped histiocytes and Touton giant cells.
We favored the diagnosis of eruptive AXGs, described previously as the presence of more than 5 yellowish papules and nodules over the body [2]. AXG usually occurs in men, at a ratio of 1.6:1, and more than 90% of the time, the lesions are found on the trunk, followed by the head and neck.
It has been reported on the extremities, albeit rarely. The demographic fits our patient well, and the biopsied specimen confirms the diagnosis of AXG.
Because XG in adults is uncommon, the diagnosis might not be immediately obvious. Dermoscopy can be employed to help differentiate it from other diagnoses on the differential, such basal cell carcinoma or sebaceous hyperplasia [4]. On dermoscopy, XGs, particularly the juvenile type, have been described as looking like a "setting sun" [5]. This orangeyellow color is not typical of the yellow "popcorn" appearance of sebaceous hyperplasia. The vessels in sebaceous hyperplasia also differ from XGs. Sebaceous hyperplasia has crown vessels [4]. Furthermore, XGs may have what look like arborizing vessels, as seen in basal cell skin cancer. However, XGs will have a more yellow-orange hue on dermoscopy than one might find in a basal cell carcinoma (BCC) and may