In the diagnosis of pityriasis alba its signs and symptoms must be analysed to arrive at the differential diagnosis to exclude other conditions and infections.
Signs and symptoms of pityriasis alba
Pityriasis alba is an asymptomatic, self-limiting and benign lesion.
It usually appears on kids of the age 3 -16 years.
The lesions are usually limited to face, especially cheeks, around mouth and chin.
Pityriasis alba may also affect shoulders, neck and arms.
In very rare cases extensive lesions of pityriasis alba may appear all over the body.
Pityriasis alba initially appear like raised red or pink patches sometime with mild itch.
After some time these pityriasis alba patches flatten out and look pale with depigmentation, which is not total.
The spots are oval or round, about 2cm in size and appearing in several numbers.
Pityriasis alba patches have small dry scales which can be seen on closer examination.
The spots appears to worsen during cold dry conditions and flake.
In summer the patches may appear prominent due to tanning of the surrounding areas of normal skin.
These lesions are not contagious and the causative agent is not known.
Pityriasis alba resolves by itself after some time and the patches may take a long time for repigmentation.
Diagnosis of pityriasis alba
Pityriasis alba is diagnosed by taking into account its symptoms and excluding the other skin conditions and diseases by differential diagnosis.
Diagnosis of hypopigmentation to exclude the other diseases
The complete history of dermatitis in the patient is noted with especial attention to the area under investigation. Old skin injuries, marks of dermatitis and infections may show hypopigmentations and take a long time to get normal pigmentation.
The possibility of the affected area being the old hypo pigmented spot of earlier conditions has to be ruled out.
The possibility of the lesion being due to fungal infections is to be ruled out by conducting Wood's lamp test and KOH test.
Diagnosis to exclude psoriasis
The distribution of the lesions sparing scalp, knees and elbows excludes psoriasis.
Diagnosis to exclude vitiligo
In vitiligo the depigmentation is complete and it is usually a progressive condition. On the face usually the areas around the mouth and eyes are affected and margins are marked. There is no scale formation.
Diagnosis to rule out nummular dermatitis
Nummular dermatitis can be ruled out by its characteristic intense itch.
Nevus depigmentosus is present from birth and is stable.
If the diagnosis is pityriasis alba, relax and follow the skin care efforts given in the treatment post.