Common Dermatoses in Children Referred to a Specialized Pediatric Dermatology Service in Mexico: A Comparative Study between Two Decades

Background. Skin diseases among pediatric patients differ from those in adults. Epidemiological studies are scarce, and those performed in Mexican population date back thirty years. It is likely that these diseases might have changed their frequency. Material and Methods. Retrospective study in first-time patients referred to a pediatric dermatology service between January 1994 and December 2003. Demographics and diagnosis were recorded and compared with the results of a previous study performed in the same institution. Results. We included 5250 patients (52.55% female, 47.47% male) with 6029 diagnoses. The most frequent dermatoses found were atopic dermatitis (14.59%), viral warts (6.62%), acne (5.53%), pityriasis alba (3.98%), melanocytic nevi (3.85%), xerosis (3.57%), keratosis pilaris (3.19%), seborrheic dermatitis (2.37%), hemangioma (2.26%), and papular urticaria (2.24%). Most dermatoses increased their frequency when compared to the previous study. Conclusion. The frequency of pediatric dermatoses in our institution has changed in the last two decades. Environmental and sociocultural factors and institutional policies might account for these results.


Introduction
Skin diseases represent between 6% and 24% of pediatric consultation [1][2][3]. Skin diseases epidemiology in children and adolescents differ from that in adult patients because several diseases are exclusive to childhood. In addition, their manifestations, diagnosis, and treatment sometimes are also different. There are few studies on the epidemiology of skin diseases in children, and even fewer have explored timely changes in the patterns of such diseases [3][4][5][6][7][8][9][10]. In spite of the fact that such studies have been conducted in countries with different ethnic, environmental, and socioeconomic conditions, some dermatoses are frequent in all populations, such as infectious (warts and impetigo) [4,10], atopic dermatitis [5,11], genetically determined (keratosis pilaris) [6,7], parasitic (papular urticaria, scabies, and pediculosis) [9], environment related (pityriasis alba) [9], and acne [9].
The frequency of skin diseases in a referral Mexican pediatric hospital population was first reported by our group in 1977 [12] in 10,000 patient referrals for skin conditions. In this study, the most common dermatoses in pediatric patients of 0-17 years old were papular urticaria (16.3%), atopic dermatitis (12.9%), viral warts (8.4%), impetigo (6.8%), pityriasis alba (6.6%), vitiligo (2.6%), acne (2.4%), diaper rash (2.0%), hemangiomas (1.8%), and melanocytic nevi (1.8%). It is worth noting that many diseases have been described only recently, and some others have decreased in frequency or have disappeared due to recent advances in prevention and treatment. We therefore sought to determine the current prevalence of skin diseases in children and adolescents attending the Dermatology Service of the Instituto Nacional de Pediatría in Mexico City, which is a large tertiary care referral center serving a population catchment area of approximately eighteen million. The secondary objective was to compare the current prevalence with the one previously reported in our institution [12] to evaluate changes in the patterns of skin diseases.

Methods
We conducted a retrospective analysis of all consecutive patients between 0 and 18 years of age that were referred for the first time to the Dermatology Service of the Instituto Nacional de Pediatría in Mexico City between January 1994 and December 2003. Information on age, gender, and diagnosis was collected from the files and consultation registry of our service. Patients with incomplete information were excluded from the study. Information was introduced in a computerized database for posterior analysis. Patients were grouped according to gender and age group divided as follows: newborns (<1 month), infants (1-12 months), toddlers (13-24 months), prescholars (25 months-6 years), scholars (>6-12 years), and adolescents (>12-17 years).

Statistical Analysis.
The frequencies of specific diagnoses were grouped by age and sex and compared to the frequency previously reported in similar age groups [12], using 2-by-2 contingency tables. The proportions were compared using a chi-squared test with Yates' correction. A P value <0.05 was considered statistically significant.
The more common diagnoses in the whole group and distributed by age and gender are shown in Tables 1, 2, and 3 together with the comparison with the frequency reported in the previous study [12]. In the whole population, the most frequent dermatosis was atopic dermatitis (14.6%) followed by viral warts (6.6%), acne (5.5%), pityriasis alba (4.0%), and melanocytic nevi (3.8%). All these conditions had a statistically significant increase in their frequency compared to the previous study (P < 0.01); on the contrary, there was a significant decrease in the frequency of papular urticaria (16.3% versus 2.24%; P < 0.01) ( Table 1). No significant changes were observed in the frequency of dermatoses in newborns. In infants, toddlers, prescholars, and scholars, there was a change in the most frequent dermatoses; in the previous study, the most frequent diagnoses were infectious or parasitic, whereas in the present study, atopic dermatitis was the most frequent disease in these age groups. Acne continued to be the most frequent cause of consultation in adolescents ( Table 2). In addition, some differences were observed between genders. Seborrheic dermatitis, papular urticaria, and miliaria were more frequent among males, whereas hemangiomas and scars were more frequent among females (Table 3).

Discussion
The data in the present work is representative of the Mexican pediatric population referred to a service specialized in pediatric dermatology; however, it is necessary to consider that many common skin diseases, such as diaper rash and chickenpox, are frequently diagnosed and treated in the primary care setting or in other specialized services, which might result in a lower observed frequency within a specialized dermatology service when compared to open population.  Atopic dermatitis was the most frequent dermatosis among all age groups, and compared to the previous study, we observed a significant increase in the prevalence of atopic dermatitis in infants, toddlers, prescholars, and scholars. We believe that this is due to the fact that atopic dermatitis is observed and/or diagnosed early. It is also worth noting that the most frequent dermatoses in these age groups in the previous study were parasitic; therefore, it is possible that improvement in sanitation, housing, and socioeconomic status might have contributed to these changes. Such changes are most likely a reflection in the national gross domestic product per capita which increased more than four times between 1975 and 2003. Warts are a common dermatosis around the world. The frequency of warts in our study was similar to that in other studies [4] conducted in otherwise healthy population. This is interesting because since our hospital is a national referral center, a substantial proportion of our patients have associated diseases which can affect immunity. The lack of difference between our study and other previously published works might suggest that in our patients such diseases were not a predisposing factor for warts; however, because information about other diseases in our children was unavailable, this is still speculative. It is important to mention that awareness about dermatologic problems has increased in many services in this hospital resulting in more frequent referrals. Pityriasis alba was the fourth most frequent dermatosis observed in our study although its prevalence in open population might be higher, and it might be underrepresented in our patients. However, a recent study conducted in a general practice setting in The Netherlands showed that in their population pityriasis alba was not a frequent diagnosis, and although the characteristics of their population might explain this difference, it is noteworthy that the study included a substantial proportion of nonwestern immigrants [10]. Hemangiomas are the most frequent benign tumors in children with an informed frequency of 2.5% in newborns and a male-to-female ratio of 3 to 1 [13]. In the present study, that hemangiomas represented 2.25% of dermatosis in the whole population and 12.96% in newborns with a male-tofemale ratio of 2.88 to 1, similar to that previously described by other authors [13].
Not surprisingly, acne was the most frequent dermatosis among adolescents with no differences between genders or compared to the previous study. Contact dermatitis is more frequent in adult patients, since it is related to exposure to chemicals; notwithstanding this, its frequency in our population was 1.48% with the adolescents and scholars being the most affected groups. Neurofibromatosis presents in 1/(3,000-4,000) population [14]. In our work, we observed it in 1.39% which was higher than the previous study. Postinflammatory hyperpigmentation was among the most frequent conditions in our study. Even though this is a sequel to other dermatoses and it is usually difficult to establish the initial diagnosis, it indicates that the skin of our patients which is usually dark has a higher predisposition to developing this change after inflammatory processes. Scars are also secondary processes, and they were the fourteenth place (1.64%). This group included patients with hypertrophic and keloid scars, secondary to surgery, burns, acne, and other conditions. The higher frequency that was observed compared to the previous study might be explained because in recent years our hospital conducted studies for scar treatment. Dermatophytoses were the eighteenth most frequent dermatosis in our patients (1.39%). Even though there was a significant decrease in dermatophytoses as a group compared to the previous study, this was due to a decrease in tinea capitis (16% in our study), whereas the cases of tinea pedis (58.6% in our study) actually increased in adolescents and scholars, probably due to changes in footwear. Tinea corporis-tinea cruris comprised 25.3% of the total cases of dermatophytoses. Vascular malformations comprise a vast group of alterations characterized by the presence of aberrant vessels. In our study, these were the twentieth most frequent dermatosis. Its incidence, as well as that of hemangiomas, was higher than that reported by other groups probably because our institution is a referral center for these conditions. Some potential limitations to our work should be noted. First, even if the number of patients is large, a substantial proportion of them had to be excluded because of incomplete information. Additionally, due to the retrospective nature of the study, it was not possible to analyze variables that could have been important such as comorbid conditions. Nevertheless, the information obtained is invaluable to realize that there have been important changes in the frequency of dermatoses in our population since the previous study. The epidemiology of skin diseases at the Instituto Nacional de Pediatría in Mexico City has modified in the last 30 years. Atopic dermatitis is currently the most frequent pathology, whereas the infectious and parasitic diseases have decreased significantly. These observations are consistent with similar studies in other countries [10]. Changes are probably related to improvement in sanitation and access to health services, and also environmental and weather variation might have played an important role. It is also possible that modifications in the institutional policies might be related to the findings. The observed changes suggest that it is necessary to modify the current strategies for education, prevention, and health care practice in order to provide patients with an optimal management.