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Dear Editor,

Psoriasis in childhood is a well-recognized entity and is distinct from adult psoriasis. Little is known on the effects of ethnicity on patterns of childhood psoriasis in Asians. To elucidate the clinical characteristics of childhood psoriasis in our multi-ethnic Asian population, we conducted a retrospective study on 315 consecutive patients under the age of 16 years diagnosed with psoriasis at our center between January 2002 and December 2009; data was extracted from patients’ medical records. The Wilcoxon–Mann–Whitney test was used to test the difference in continuous measurement and Fisher’s exact test was used for categorical data.

The majority were female (183, 58.1%). Chinese, Malay, Indians and patients of other ethnicity comprised 144 (45.7%), 83 (26.4%), 61 (19.4%) and 27 (8.6%) patients, respectively. The proportion of Indians differs significantly from the general ethnic distribution of Singapore (9.2% Indian). The mean age at onset of psoriasis was 7.7 years (range, 0.08–16 years). Fifty-four patients had a positive family history, with 79.6% (43 patients) in first-degree relatives (15 mothers, 21 fathers, seven siblings). This was not associated with a younger age at onset. Malays formed the highest proportion (22.9%) with a positive family history.

The scalp was the most frequently involved site at the time of first presentation in all ethnicities (Table 1). Malays and Indians had significantly more scalp involvement than Chinese or patients of other ethnicities (P < 0.001). Indians had a significantly lower rate of involvement of the buttocks or perineum (3.3%, P = 0.002).

Table 1.   Distribution of psoriatic lesions at first presentation among different ethnic groups (%)
 Chinese (n = 144)Malay (n = 83)Indian (n = 61)Other ethnicities (n = 27)Total (n = 315)P-value*
  1. *Fisher’s exact test is used to compare the psoriatic lesions at first presentation among ethnic groups.

Scalp53.577.178.755.664.8<0.001
Nails47.230.132.829.638.40.034
Extensor limbs36.839.831.244.437.10.609
Trunk30.634.923.037.030.80.389
Face13.230.116.429.619.70.009
Ears13.226.516.411.117.10.076
Buttocks or perineum15.324.13.325.916.20.002
Axilla6.36.04.93.75.71.000
Neck5.68.44.905.70.511
Palms or soles6.31.26.67.45.10.202

Chronic plaque psoriasis was the most prevalent subtype at first presentation in all ethnicities (54.3%); guttate psoriasis was rare (Table 2). Twenty-four patients had isolated nail involvement. Significant predilection for this nail subtype occurred in Chinese patients (P = 0.001). Arthropathy was noted in one Malay patient with generalized pustular psoriasis.

Table 2.   Distribution of subtype at first presentation among different ethnic groups (absolute number and %)
Subtype*Chinese (n = 144)Malay (n = 83)Indian (n = 61)Other ethnicities (n = 27)Total (n = 315)
  1. *Chronic plaque: sharply-defined, erythematous, scaly plaques symmetrically distributed on the trunk, buttocks (not including the intergluteal cleft), limbs or any combination of the above-mentioned areas in Table 1. Sebopsoriasis: salmon-pink to erythematous, discrete, scaly plaques of varying size or less well-defined plaques with more greasy scaling involving the scalp, hairline, face or ears. Inverse: shiny pink to erythematous, sharply-defined, thin plaques isolated to the intergluteal cleft, perineum, axilla or neck. Nail: pitting, subungual hyperkeratosis, distal onycholysis and the “oil drop” phenomenon of fingernails or toenails. Acute guttate: showers of discrete 2 mm to 1 cm round or oval erythematous scaly plaques in a generalized distribution. Generalized pustular: painful pustules on erythematous base in a generalized distribution, with general malaise and fever. Palmoplantar plaque-type: sharply-defined scaly plaques without vesiculation involving the palms and soles. Palmoplantar pustulosis: pustules admixed with yellow-brown macules on the palms and soles.

Chronic plaque76 (52.8)50 (60.2)29 (47.5)16 (59.3)171 (54.3)
Sebopsoriasis38 (26.4)27 (32.5)25 (41.0)7 (25.9)97 (30.8)
Inverse2 (1.4)2 (2.4)1 (1.6)05 (1.6)
Nail20 (13.9)1 (1.2)1 (1.6)2 (7.4)24 (7.6)
Acute guttate3 (2.1)1 (1.2)1 (1.6)05 (1.6)
Generalized pustular1 (0.7)1 (1.2)1 (1.6)1 (3.7)4 (1.3)
Palmoplantar plaque-type2 (1.4)1 (1.2)2 (3.3)1 (3.7)6 (1.9)
Palmoplantar pustulosis2 (1.4)01 (1.6)03 (1.0)

Topical steroids, coal tar, phototherapy, methotrexate, acitretin and biologics (etanercept and ustekinumab) were received by 304, 224, 20, six, eight and one patient, respectively. None received cyclosporin. Hyperlipidaemia prior to, during and after acitretin treatment was noted in two female patients who had generalized pustular psoriasis.

This study revealed unique characteristics of childhood psoriasis amongst Asians, both comparable to and distinct from previous studies.

The female preponderance (male : female, 1:1.39) is consistent with studies from the Middle East (1:1.5)1 and Denmark (1:2),2 whereas Indian,3 Chinese4 and Australian5 studies showed no sex difference. In contrast, adult-onset psoriasis occurs nearly equally in males and females.

The average age at onset in other Asian and Caucasian populations is 9.1–10 years3,4 and less than 5 to 8.1 years, respectively, suggesting that Asian children develop the disease later. In comparison to our data, a high familial incidence (up to 59%) has been reported in Caucasians.2,5 The predominant scalp involvement is in concordance with published data.1–4

Divergent distribution of human leukocyte antigen (HLA) and other genetic determinants may account for the clinical differences amongst ethnicities. Little is known on the genetics of psoriasis in Indians; it is associated with HLA-A1, -B17 and -Cw6.6 A higher incidence of psoriasis occurs locally in the Indian subgroup, and Singaporean Indians with psoriasis have twice the risk of developing psoriatic arthritis compared to Chinese with psoriasis.7 In contrast, the genetics in Han Chinese has been extensively investigated, demonstrating association of ERAP1 and ZNF816A with early-onset psoriasis. PSORS4 is associated with psoriasis in Singaporean Chinese.8

The predominance and rarity of the chronic plaque and guttate subtypes, respectively, has been described. The particularly low prevalence of guttate psoriasis in our population (1.6% vs 6.4–44% in other studies)1–5 could be explained by our center being a tertiary referral unit; more patients could initially be treated by primary care.

In the general psoriatic population, patients with nail psoriasis have more severe and longer disease and poorer quality of life.9 A high clinical index of suspicion should be present for Chinese who present with isolated nail abnormalities.

The rate of metabolic comorbidities in psoriatic patients aged less than 20 years is twice that of non-psoriatics.10 The prevalence of metabolic syndrome in childhood psoriasis is unknown. Perhaps there lies a role for routine metabolic screening in children with psoriasis, in particular, those manifesting more severe subtypes.

As this study was not population-based, a referral bias exists. Its retrospective nature adds recall and interviewer bias. Diagnoses were made clinically; only two skin and no nail biopsies were performed.

Awareness of the characteristics of childhood psoriasis will aid clinicians in early diagnosis and management. Further work into the genetics amongst Asians is required.

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