Final answer:
An insensate hypopigmented patch of skin in an Asian patient most likely suggests Hansen's disease (leprosy), caused by Mycobacterium leprae, and characterized by nerve damage and loss of sensation. Other conditions like vitiligo and contact dermatitis would generally not exhibit sensory loss.
Step-by-step explanation:
In an Asian patient with an insensate hypopigmented patch of skin, you should suspect Hansen's disease (leprosy). This infectious disease is caused by Mycobacterium leprae and is characterized by blanched, numb areas on the skin. The immune response of the patient determines the extent of the disease, which can range from tuberculoid (paucibacillary) Hansen's disease, with few lesions and an effective immune response, to lepromatous (multibacillary) Hansen's disease, where there's more widespread disease with nodules filled with acid-fast bacilli and macrophages. The damaged peripheral nerves result in a loss of sensation which can lead to serious complications like ulcers and loss of extremities due to unperceived injuries.
Vitiligo is characterized by depigmentation, but it is not typically associated with loss of sensation. Contact dermatitis would usually be itchy or painful, not insensate. Similarly, psoriasis typically presents with inflamed, scaly skin and not with insensation.
Diagnosis is based on clinical signs and confirmed by the presence of acid-fast bacilli in skin smears or biopsy specimens. M. leprae is difficult to culture in vitro, but it can be identified by culturing in vivo or by PCR and genotyping of DNA in tissue samples.