What Causes White Patch On Lower Abdomen Extending To Back?

Sir This is Miss Indrani Das.I am a resident of Kolkata.I am 28.Since my birth i have a white patch on my skin at lower abdomen of size about 12 cm * 5 cm which extends from lower abdomen to back nearly touching spinal chord.On consultation Dr. Subrata Malakar said this is not a case of vitiligo.He opined that since it is a birth mark no surgical remedy is possible on that patch.No proper treatment or diagonostic test has been done yet.I am going through lot of mental pressure and distress.I cannot even wear a sari for this problem. Please advice to get rid of this problem. Yours Faithfully, Indrani Das