flat aSx symmetrical well demarcated areas of depigmentation (loss of melanocytes)
esp on limbs or around face (esp periphery)
may resolve, may progress .... show Koebner phenomenon
poliosis - involves hair, halo naevi, 

autoimmune therefore do ANA, Thyroid, Haematinics ?? DM PA Addisons alopecia areata
genetic - 1% of world population - Sx by 20-30yrs

DD - fungal, Pityriasis Alba

Mx - difficult as only 30% success with anything
cosmetic camouflage and suncream impt
topical steroids, UV, Protopic