Erythema ab igne (EAI) is a localized skin lesion characterized by areas of reticulated erythema and hyperpigmentation. It is caused by prolonged and repeated exposure to heat (infrared radiation). The course of the lesion started with evanescent net-like erythema or transient reticulated macular erythema, it associated with slightly increase in skin temperature. After repeated heat exposures, the reticular erythema turn out to be persist and, later, finally it become gradually hyperpigmented [1,2]. Although the pathophysiology of this condition is poorly understood, There are some theories that may explain it. One of them is chronic heat exposure can causes damage to the epidermis and superficial vascular plexus due to cutaneous hyperthermia. In vitro study has been reported that moderate heat had synergistic effect with ultraviolet radiation to denature DNA in squamous cells [3]. Another explanation is dilation and deposition of hemosiderin in a reticulate distribution of the injured superficial blood vessels due to prolonged heat exposure [2]. Many heat sources may lead to this condition such as hot water bottles, heating blankets or heat pads, heated car seats, space heaters, or fireplaces. In the last decade, there was markedly increase in the use of the modern technology, laptop computers is one of these technology that has been implicated as the modern cause of Erythema ab igne [4]. So according to this different causes, Erythema ab igne is also termed hot water bottle rash, fire stains, laptop thigh [5,6].

The diagnosis of erythema ab igne is based on the history and clinical picture. A history will typically reveal prolonged and repeated exposure to thermal radiation at level lower than that which causes a thermal burn [1]. If the diagnosis of erythema ab igne is uncertain, we can perform a 3-mm or 4-mm punch biopsy, the histopathological findings depend on multiple parameters; the type of heat, the length of exposure, and the area of the body involved. Histologically, it is mimic solar-damaged skin, demonstrating in early lesions epidermal atrophy, then hyperkeratosis, melanin incontinence with abundant melanophages in dermis, and elastic fibre alterations [4]. Until now, there is no definitive treatment for erythema ab igne. In the management of erythema ab igne, start with non-pharmacological approach by eradicating the heat source. On the one hand, early removing of the heat source will give good prognosis that may resolute the reticulated erythema within more than a few months. On the other hand, chronic exposure to the heat source can cause permanent hyperpigmentation and may need tretinoin, and 5-fluorouracil cream to clear epithelial atypia [7,8]. Unfortunately, there is risk of malignant transformation with chronic erythema ab igne [9].

Moreover, there are still gaps in knowledge regarding this dermatological condition, especially the more recent one, Laptop computer-induced erythema ab igne. Our aim was to systematically review case reports of laptop computer-induced erythema ab igne, in order to outline the main features of it and increase the knowledge about this new skin condition.

We reviewed all cases of laptop computer-induced erythema ab igne from the first published case in 2004 to December 2013 using the online databases of PubMed, MEDLINE, Trip database, and Google Scholar. We limited our search only to those studies involving case reports publication type, but we did not restrict the search by country of publication or publication dates or language.

The electronic search strategy was as follows: (laptop[All Fields] AND ("computers"[MeSH Terms] OR "computers"[All Fields] OR "computer"[All Fields])) AND induced[All Fields] AND (("erythema"[MeSH Terms] OR "erythema"[All Fields]) AND ("abnormalities"[Subheading] OR "abnormalities"[All Fields] OR "ab"[All Fields]) AND igne[All Fields]) AND ("case reports"[Publication Type] OR "case report"[All Fields])

We screened the titles and the abstracts of the articles that found during the search and excluded any that were considered irrelevant or not a case report. We also checked the references of all obtained literature and all included papers to identify any further possibly related studies.

The table below illustrates some of the main characteristics of the all case reports that we were reviewed:

Table 1: Main characteristics of the all case reports.

Erythema ab igne (EAI) is a reticular erythematous pigmented dermatosis consequential from repeated exposures to infrared radiation or reasonable heat in the range of 43-47ºC; it is usually insufficient to bring into being a burn [2]. It can arise at any site of the skin of the body depending on the heat or radiation source, usually it occur in an asymmetrical distribution corresponds to the different sources of heat that are currently in use [4].

Previously, EAI was first started as an occupational disease in the shins who work nearly to heat source such as open fires or coal stoves. Recently, the typical EAI has been declined in this group of populations due to use of central heating [29]. In the other hand, it has been notice in the individuals who appliance of heating pads on the back or the abdomen to decrease the chronic pain [5]. In the more recent, with increase the modern technology, the rising incidence of the use of electronic devices which can generate thermal radiation that may cause Erythema ab igne [15].

In our review of the literature, there are 22 case reports of laptop induced erythema ab igne from different countries; Netherland, France, India, America, Turkey, Italy, Sweden, Switzerland, Canada, Brazil, Spain, and Germany [2,10-29]. In these reports, 13 of the 22 patients were females (62%), while 8 of the 22 patients were males (38%) (Figure 1).

Figure 1: Showing the composition of males and females.

The average age is 23.5 years when the condition was discovered. The site of the erythema ab igne lesion is corresponding to the area of contact with the laptop’s heating element. The majority of the laptop induced erythema ab igne cases located on the thighs (20 of 22 cases, 91%) (Figure 2). Over half of those cases reported that the lesion is predominantly on the left thigh (13 of 22 cases, 65% on the left thigh, while 4 of 22 cases, 15% on the right thigh, and 3 of 22 cases, 20% on the both thighs).

Figure 2: Showing location of the lesion in Thigh, Breast and Abdomen.

(Figure 3) There is only one report of laptop induced erythema ab igne located in left breast for 18-year-old girl who was use of her laptop computer while reclining [24]. There is another one report of laptop induced erythema ab igne located in left side of the abdomen for a 20- year-old male engineering student who had the habit of placing the laptop computer on the bare skin of his abdomen [26].

Figure 3: Showing the Location of the lesion predominantly on the thighs.

Almost all of the laptop induced erythema ab igne cases were asymptomatic macular, erythematous and hyper pigmented, reticulated lesion except one case that was associated with burning and itching [19]. The duration of laptop exposure ranged from two weeks to two years (Figure 4).

Figure 4: Showing duration of the laptop exposure.

Biopsy was not frequently performed. In fact, in case of laptop computer induced erythema ab igne the diagnosis is easily made by history and direct examination [1]. Biopsy would be most useful in chronic erythema ab igne, while in patients who are in risk of malignant transformation [9].

Limits in our results are due to incomplete information in the cases about the exact duration of laptop exposure and the duration and frequency of the daily use of laptop. Actually, 50% of the reports did not mention the exact duration of laptop exposure. (Figure 4) Moreover, publication bias is a potential problem in systematically reviewing case reports. Lack of publications about the laptop computer induced erythema ab igne during two years; 2005 and 2008, hence it is not possible to rule out present of this condition during this period. (Figure 5) Unfortunately it was not possible to extract from the case reports the type of the laptops.

Figure 5: Showing the year of publication.

Erythema ab igne is a localized reticulated erythema and hyperpigmentation lesion by prolonged and repeated exposure to heat. Laptop computer induced erythema ab igne is increasing in the last years. One of the important questions in evaluation erythema ab igne patients are about the history of prolongs laptop exposure. We recommend awareness programs development in the future to laptop users about this condition and advise them to avoid placing laptops on their body for prolonged periods of time and direct them to place laptops on a solid barrier.