We read with interest the work by Cayuela et al. on the effect of age on the incidence rate of psoriasis in Spain.1 Although the authors limited their study to data from 1990 through 2019 and commented on its bimodal distribution – confirming a higher prevalence of earlier-onset psoriasis in women – we were struck by the lack of a thorough review of national references, particularly those published in Actas Dermosifiliográficas. This omission has also occurred in other similar studies previously conducted in the country,2,3 which we presume may be due to limited indexing.
In 1988 we published in this journal a study of 2523 cases analyzing age at onset and familial involvement in psoriasis.4 All psoriasis cases recorded over a 26-year period (1961–1986) from the Departments of Dermatology I and II of the Hospital Clínico San Carlos (Madrid, Spain) were analyzed. At that time, our Professors Antonio García-Pérez and Francisco Sánchez de Paz already referred to “the psoriasis,” considering it properly a syndrome.
Among several conclusions, the two peaks of onset were confirmed: the first at 14.48±12.62 years in women and 21.81±13.37 years in men, and the second at 49.45±9.48 years in women and 45.42±14.15 years in men. Age at onset was significantly lower in women (P<.0001). According to age interval, the sex distribution showed a predominance of women (19.14%) over men (9.53%) between 0 and 9 years of age (P<.0005).
Although not consistently, several Western studies have reported similar findings, with approximately twice as many girls as boys affected during childhood, or a predominance of girls across all 0–15-year age intervals for age at onset.4 This observation has also been demonstrated in other populations and ethnic groups. For example, in a series of 1366 cases from Sri Lanka, a significant difference of 9.2 years in earlier onset in women was reported.5 Much earlier, Hoede (1931) had already reported an earlier age of onset in women based on 959 cases, and Romanus (1945), in an analysis of 1417 cases, determined that half of the men were affected before the age of 19 and three quarters before 26, whereas half of the women developed the disease before the age of 12 and three quarters before 19.6 Due to limitations in the number of references allowed, we did not include other series with similar findings.
Other relevant data from our study showed that when either the father or mother had psoriasis, the disease began before the age of 30 in almost 79% of cases. In this same age group, the proportion of familial involvement doubled compared with the group whose disease began after that age (25.4% vs 12.5%). We detected a higher frequency of familial involvement in men (21.58% vs 17.49%) across all age intervals. However, when this variable was analyzed according to age at onset by sex, the lowest mean age was observed in women with familial involvement (men 25.76±14.73 years and women 19.53±14.87 years).
In China, a study of the Han population including 1043 psoriasis cases showed that the peaks of onset were between 30 and 39 years in men and between 10 and 19 years in women. When one or both parents were affected, the mean age of onset was also earlier in women.7 In Korea, an analysis of 5084 psoriasis patients found that the age of onset in men was around 20 years, whereas in women it occurred during adolescence. It was also observed that more women than men had a family history of psoriasis, and that its frequency was higher when the age of onset was before 30 years.8 Another study in Japan involving 1120 patients also demonstrated a bimodal distribution, with the first peak around 30 years in men and around 10 years in women. Furthermore, when the sample was stratified according to age at onset, the frequency of familial involvement was higher in women whose disease began before 30 years (15.4%) than in those with later onset (5.3%). The authors suggested that in the former group there may be a greater influence of genetic predisposition factors rather than environmental factors in the development of the disease.9 Moreover, it has been concluded that significantly earlier onset before the age of 20 occurs when the father is affected, whereas maternal influence appears mainly in the 20–29-year age interval.10
As Cayuela et al. also suggest, we believe that future studies should carefully analyze early- and late-onset cases separately.1 In addition, all possible variables should be compared according to sex, age at onset in short intervals, and familial involvement (including parental age at onset and affected siblings) to determine the influence of possible sex-related genetic determinants, particularly in early-onset cases.
