Velderix Riehn'va ("The Usurper") is a neurological disease that affects Romulans. The disease progressively weakens artery walls in the brain, resulting in the individual suffering fatal aneurysms.

In 2381 and 2382, Alizome infected Xarian Dor and Tal'Aura with Velderix Riehn'va, causing the deaths of both. Alizome, who was unaffected by the disease as she was Tzenkethi, had passed the disease onto both by casual contact such as shaking hands. (ST - Typhon Pact novel: Rough Beasts of Empire)