Clinical Definition and Overview
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Pityriasis alba (PA) is a disorder of mild cutaneous inflammation resulting in disordered pigmentation characterized by asymptomatic hypopigmented macules, patches, and thin plaques with fine scale on the face, neck, upper trunk, and proximal extremities of children and young adults.
Scarcely prevalent in adults, PA affects an estimated 5% of the pediatric population and is among the most common disorders of hypopigmentation seen in children. While people of all skin types and ethnicity are affected, it is more obvious in those with more darkly pigmented skin.
Given its asymptomatic and generally limited nature, only a portion of individuals with pityriasis alba seek treatment. In many cases, however, areas of hypopigmentation are readily obvious and cause considerable distress for patients and their parents.
Strongly associated with atopy, pityriasis alba is considered a minor criterion for diagnosing atopic dermatitis.
While little is known regarding the underlying pathogenesis, the decreased pigment of pityriasis alba is considered a post-inflammatory phenomenon following a low-grade eczematous reaction.
Examination of the affected skin shows a decrease in the number of melanosomes, a characteristic finding in atopic dermatitis. Additionally, like atopic dermatitis, pityriasis alba has been linked with a loss-of-function filaggrin mutation.
Given the integral role of filaggrin in ther water-holding capacity of the stratum corneum, this explains xerosis as a frequently associated feature of both conditions.
Other associations of pityriasis alba have been investigated, with some sources suggesting that sun exposure habits, personal hygiene, and/or nutritional deficiencies are connected to the disease. While possible infectious etiologies have also been implicated, none are as of yet elucidated.
The early lesions of pityriasis alba—mildly erythematous slightly scaly thin plaques with ill-defined margins—are seldom noticed. Instead, it is the resulting hypopigmented round to oval areas that are generally of concern to patients.
Slightly elevated with fine scale, plaques may be from 0.5 to 4 cm in diameter and number from one to several lesions. The face, particularly the cheeks, is the most commonly plagued site in children, although the lateral arms, shoulders, neck, and anterior thighs may also be plagued. While uncommon, widespread involvement may occur. The lesions of pityriasis alba are typically asymptomatic, only occasionally associated with mild pruritus.
Natural History and Prognosis
If untreated, pityriasis alba tends to be a relatively chronic condition with frequent relapses and a variable course.
Although the disease most often resolves spontaneously prior to adulthood, repigmentation is a slow process that may take months to years to resolve in entirety.
Seasonal variation does occur, with plaques becoming more conspicuous in summer months when the affected sites do not tan like surrounding skin. In the dry winter months, plaques may become scaly and inflamed. Although chronic and often a cosmetic burden, pityriasis alba is not associated with any complications or permanent disfigurement.
While rarely obtained, biopsy of skin affected by pityriasis alba shows a nonspecific picture consisting of spongiosis with exocytosis, hyperkeratosis, and dermal perivascular lymphocytic infiltration.
In early stages, following plugging, follicular spongiosis, and atrophic sebaceous glands may also be seen. The quantify of melanocytes observed varies by report, with some sources suggesting fewer in number than normal skin, similar to atopic dermatitis.
Other studies indicate affected skin having a comparatively larger number of melanocytes that also appear damaged by electron microscopy. Consistently, a reduced number of melanosomes are observed in lesions of pityriasis alba.
Diagnosis and Differential Diagnosis
The diagnosis of pityriasis alba is made clinically, although certain laboratory tests (e.g., potassium hydroxide preparation) may be used to help differentiate it from other conditions. Biopsy is seldom indicated, only in specific cases when disorder such as sarcoidosis or mycosis fungoides must be excluded.
Pityriasis alba is commonly mistaken for tinea versicolor and vitiligo. In general, tinea versicolor differs from pityriasis alba in that facial involvement is less common; the hypopigmented lesions are smaller, more numerous, and often coalescing; and potassium hydroxide preparation is positive for yeast elements.
Patches of vitiligo Opens in new window are more sharply demarcated than the lesions of pityriasis alba and completely lack scale and pigment. Other disorder of hypopigmentation that should be considered in the differential diagnosis include follicular mucinosis, psoriatic leukoderma, mycosis fungoides, nevus depigmentosus, and nevus anemicus.
Patients with pityriasis alba should be counseled that lesions will slowly improve on their own with time. If mild inflammation is present, topical corticosteroids or calcineurin inhibitors (i.e., 1 % pimecrolimus cream, 0.03 % or 0.1 % tacrolimus ointment) may be used.
Other sources suggest using 01 % tacrolimus and 0.0003 % calcitriol ointments in conjunction. Unfortunately, treatment of the hypopigmentation of pityriasis alba is difficult, and it has been shown that topical steroids and emollients are of similar efficacy. With the risk for side effects from chronic corticosteroid use, it is reasonable to treat only with lubrication and sun avoidance to prevent darkening of the skin surrounding the affected areas.
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