My favourite disease: zoster
Zoster is a viral disease caused by the varicella zoster virus, the same one that causes chickenpox. VZV can remain latent in the dorsal root ganglions for years without causing any symptoms, but in beneficial situations (e.g. disturbances in the immune system due to aging, immunosuppression etc), it can break out of the nerve ganglions and travel down nerve axons infecting the corresponding dermatome.

The first symptom is usually great neuropathic pain in the affected dermatome, followed by rash and vesicles. Since the symptoms limit to a certain dermatome, the rash forms in a defined shape that appears on one side of the body and doesn’t cross the midline. Even though the vesicles will heal in a rather short time (10 days or so), they may leave deep scars. The pain can also remain for a long time after the other symptoms have ended.