idiopathic guttate hypomelanosis idiopathic guttate hypomelanosis idiopathic guttate hypomelanosis is characterised by multiple small whitish flat spots. they are typically irregular, well defined and frequently appear on the arms, legs and face of older people. idiopathic guttate hypomelanosisother namesleukopathia symmetrica progressivaspecialtydermatology it occurs in up to 80% of over 70-year olds. females may notice them at a younger age than males.