Reticulated Rash on the Bilateral Lower Extremities in an 11-year-old Girl.

Abstract

An 11-year-old girl presents with a cutaneous eruption localized to the bilateral lower extremities. The eruption first appeared 1 month before presentation, during the winter. The patient’s mother reports discrete bullae, which resolved before presentation. The child is well in all other respects. Physical examination reveals ill-defined hyperpigmented and reticulated patches on both of the anterior legs (Fig 1). Discrete hyperkeratotic nodules are present distally (Fig 2). The lesions are nonblanching and fixed. A punch biopsy sample of one of the hyperpigmented nodules on the left leg was sent for histopathologic examination and confirmed the diagnosis (Fig 3).The clinical differential diagnosis of a mottled or reticulated eruption in a child primarily includes livedo reticularis, erythema ab igne (EAI), and erythema infectiosum. Because this patient was systemically well and the cutaneous changes presented in the winter months, we initially suspected EAI. The patient vehemently denied heat exposure initially, which prompted biopsy. After histopathology supported a diagnosis of EAI, the patient admitted to regular use of a space heater.Long-term exposure to mild heat and infrared radiation can result in a benign, reticular pigmented dermatosis known as EAI. (1)(2)(3) EAI develops over the course of weeks to months from repeated skin exposure to heat below the threshold for thermal burns. (4)(5) The timing of onset depends on the degree and duration of heat exposure. The precise pathophysiology remains unknown, but it is thought that heat damages the superficial cutaneous vessels, leading to vasodilation and hemosiderin deposition, with subsequent netlike hyperpigmentation. (4)(6)Multiple heat sources have been reported to cause EAI. Historical causes include fireplaces, radiators, and wood-burning stoves. (5) More recent associations include space heaters, heating pads, laptop computers, heated car seats, and sauna belts. (3)(5)(6) Traditionally, at-risk populations have included females, the elderly, and those who experience chronic pain (4); however, as new heat sources are described, EAI is becoming more prevalent in younger patients. (3)(6)Clinically, the cutaneous eruption is characterized by mottled or reticulated erythematous patches. Early in the disease course, erythema is blanchable. Chronic exposure leads to fixed hyperpigmented patches, hyperkeratotic plaques, and even bullae. The distribution on the skin is affected by many factors, including the heat source, skin type, clothing barrier, and directions of the radiation. (7)(8) EAI most frequently appears on the anterior legs and thighs. A retrospective multicenter study of 71 patients found that 60.6% of lesions were localized on the anterior aspect of the legs. (3)(5) Patients are generally asymptomatic, but pruritus or pain can eventually develop. (4)(8)(9)EAI is not traditionally associated with bullae; however, several cases of bullous EAI have been reported in the literature, some of which were associated with diabetes mellitus, hypothyroidism, and eating disorders. (5) EAI should be considered in the differential diagnosis if a patient presents with a localized bullous eruption, particularly when reticulated patches or plaques are also present. (10)The clinical differential diagnosis of a mottled or reticulated eruption in a child also includes livedo reticularis and erythema infectiosum. The presence of facial erythema and constitutional symptoms in a younger child supports a diagnosis of erythema infectiosum. In this setting, erythematous reticulated patches appear on the extremities, wax and wane over a period of 2 to 3 weeks, then resolve spontaneously. Livedo reticularis presents with a uniform, netlike pattern on the extremities. Patches are erythematous and not hyperpigmented. Livedo reticularis can be physiologic, in which case skin changes are exacerbated by cold exposure and resolve with warming. Primary livedo reticularis is idiopathic, and lesions are fixed. Livedo reticularis can also be secondary to a systemic disease, including an autoimmune connective tissue disease, vasculitis, or a hypercoagulable state. In most cases, the practitioner can make a diagnosis of EAI and rule out alternate etiologies with a thorough history and physical examination. When the diagnosis is not clear, a skin biopsy can be helpful.EAI is generally self-limited and resolves with discontinuation of heat exposure. The healing time is inversely related to cumulative heat exposure and can range from weeks to years. (9)For patients who are asymptomatic, the use of bland emollient and sun protection can accelerate resolution and limit the potential for postinflammatory hyperpigmentation. Consider a low- to mid-potency topical corticosteroid ointment for pain or pruritus. Chronic EAI can lead to epidermal dysplasia, (11)(12)(13)(14)(15)(16) and although rare, neoplasms such as squamous cell carcinoma or Merkel cell carcinoma can develop. (1)(5) Severe or recalcitrant cases should be referred to a dermatologist or wound care specialist.The patient was treated with triamcinolone 0.1% ointment twice daily. After 6 weeks of therapy, the nodules had resolved completely and the hyperpigmented patches were nearly resolved.