This 67 years old patient had Herpes Zoster like vesicles over T1, 2 dermatome territory, and recovered without any pain medication. After 15 days, He is c/o severe pain over the healed vesicles. Although he is lean, thin emaciated body. His healed marks are, looks like psoriatic change.

The query is, what is the reason of pain? Is it a deficiency of vitB12? Is it indicative of hidden malignancy?