Association of Pityriasis Alba with Atopic Dermatitis: A Cross-Sectional Study.

Sir,

Pityriasis alba is one of the minor factor of Hanifin and Rajka's[1] criteria of atopic dermatitis. There are only a few analytical studies on the association of pityriasis alba with atopic dermatitis.[2]

We selected one-hundred-and-twenty-two consecutive patients with pityriasis alba (confirmed by two faculty members with postgraduate qualification in dermatology) and an equal number of age group and sex-matched patients with common hypopigmented disorders other than pityriasis alba (hundred patients with pityriasis versicolor, fifteen patients with post-inflammatory hypopigmentation, four patients with early vitiligo, two patients with Hansen's disease, and one patient with hypomelanosis of Ito) attending the outpatient department of dermatology of a teaching hospital during a period of 18 months for this study. The sample size was determined based on two previous studies.[34]

The clinical profile, history of associated diseases, and precipitating factors of the participants were explored. They were evaluated for atopic dermatitis using the UK Working Party's diagnostic criteria.[5] Ethical clearance was obtained from the institutional ethics committee.

The age of the patients with pityriasis alba ranged from 6 months to 20 years. One-hundred-and-twelve (92%) patients were aged less than 15 years. The gender distribution was almost equal (M:F = 1.03:1). Average daily direct sun exposure of more than two hours (P = 0.03), personal history of atopy (P = 0.004), family history of atopy (P = 0.000) were associated with pityriasis alba, whereas, washing of the affected areas more than three times a day (P = 0.12) and washing of affected areas with soap more than two times a day (P = 0.30) were not associated [Table 1]. At least one atopic feature (namely, xerosis, ichthyosis, hyperlinearity of palms, recurrent conjunctivitis; hand and foot dermatitis, nummular eczema, pompholyx or Dennie Morgan folds) was seen in one-hundred-and-fourteen (93.4%) cases compared to sixty-six (54.1%) controls (P = 0.000). Among the individual atopic features, hyperlinearity of the palms (P = 0.000), xerosis (P = 0.000), and ichthyosis vulgaris (P = 0.000) were associated with pityriasis alba. Five patients (4.1%) with pityriasis alba satisfied diagnostic criteria of atopic dermatitis, whereas none in the control group did so. (P = 0.03). On multivariate logistic regression, significant association was noted for family history of atopy (P = 0.00), presence of at least one atopic feature (P = 0.000), xerosis (P = 0.000), ichthyosis (P = 0.000), and hyperlinearity of palms (P = 0.000) [Table 2].

Table 1

Clinical features of patients with pityriasis alba compared to the control group

Clinical features	Number of patients among cases (n=122) (%)	Number of patients among controls (n=122) (%)	Chi square	P	Crude odds ratio	Confidence interval Lower, upper
Exposure to direct sun exposure for more than 2 h a day	52 (42.62)	38 (31.15)	3.451	0.03 (one tailed); 0.06 (two tailed)	1.639	0.9694, 2.785
Washing of the affected area more than 2 times a day with soap	6 (4.91)	10 (8.1)	0.30	1.07	0.5806	0.1899, 1.657
Washing of the affected areas more than 3 times a day	119 (94.26)	122 (100)	3.03	0.12 (mid P exact)	0	0, 1.704
Personal history of atopy	27 (22.13)	11 (9.01)	7.97	0.004	2.856	1.361, 6.287
Family history of atopy	61 (50)	19 (15.57)	32.80	0.000	5.381	2.967, 10.04
Dennie Morgan fold	2 (1.63)	0 (0)	2.017	0.4979 (Fisher exact)	undefined	0.2885, ‘undefined
Hyperlinearity of palms	78 (63.93)	46 (37.70)	16.79	0.000	2.915	1.737, 4.938
Xerosis	110 (90.16)	44 (36.06)	76.69	0.000	16.03	8.115, 33.51
Ichthyosis vulgaris	47 (38.52)	8 (6.55)	35.7	0.000	8.852	4.086, 21.07
Nummular eczema	3 (2.45)	0 (0)	3.037	0.2469 (Fisher exact)	undefined	0.5869, ‘undefined
Pompholyx	2 (1.63)	1 (0.8)	0.3375	1.00	2.011	0.1513, 59.95
Hand/foot dermatitis	5 (4.09)	0 (0)	5.105	0.0599 (Fisher exact)	undefined	1.241, ‘undefined
Recurrent conjunctivitis	1 (0.8)	3 (2.45)	1.017	0.6218 (Fisher exact)	0.3292	0.01236, 3.132
Presence of any one of the atopic features	114 (93.4%)	66 (54.1%)	48.8	0.000	11.97	5.553, 28.38
Patients satisfying Hanifin and Rajka criteria for atopic dermatitis	5 (4.1%)	0 (0%)	5.105	0.03 (Fisher exact)	undefined	1.241, undefined

Table 2

Multivariate logistic regression analysis of predictor variables

Variable	Crude odds ratio	Lower limit	Upper limit	Adjusted odds ratio	Lower limit	Upper limit	P
Exposure to direct sun exposure for more than two hours a day	1.25	0.82	1.91	1.60	0.89	2.86	0.112
Washing of the affected area more than two times a day with soap	0.6	0.21	1.65	0.57	0.19	1.71	0.325
Personal history of atopy	1.62	0.87	3.02	1.87	0.94	3.73	0.073
Family history of atopy	2.4	1.50	3.82	3.32	1.94	5.71	0.00
Xerosis	2.5	1.76	3.54	8.27	4.59	14.91	0.00
Ichthyosis vulgaris	5.875	2.77	12.43	9.24	4.10	20.85	0.00
Pompholyx	2	0.18	22.05	2.04	0.18	22.70	0.56
Hyperlinearity of palms	1.69	1.17	2.44	2.47	1.54	3.97	0.00
Recurrent Conjunctivitis	0.33	0.03	3.20	0.337	0.03	3.28	0.349
Presence of any one of the atopic features	1.72	1.27	2.33	4.21	2.49	7.10	0.00

We found an association between pityriasis alba with personal history and family history of atopy (especially in first-degree relatives) as reported by Vinod et al.[6] Some descriptive studies have reported a higher frequency of atopic dermatitis in patients with pityriasis alba.[367] Weber et al.[2] had reported an association between pityriasis alba and atopic dermatitis in a comparative analytical study. Our study confirms such an association using a larger sample size. The co-existence of at least one atopic feature, especially xerosis, ichthyosis, or hyperlinearity of the palms could support a diagnosis of pityriasis alba in a patient with compatible clinical features.

Limitations of our study include recall bias among patients and selection bias expected in a hospital-based study. Adequate sample size, analytical design, and multivariate analysis are some of the strengths of this study. Future studies with large population data may throw more light on the association of pityriasis alba with atopic dermatitis.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.