What are the effects of encephalitis on the hypothalamus?

Varies: If encephalitis spreads to the hypothalamus it is hard to predict, because there are many nuclei or "centers" in the hypothalamus that do very different and sometimes opposite functions. For example some people with encephalitis lethargica slept constantly while others could not fall asleep at all, because different nuclei were affected.

Hard to answer: Certain forms of encephalitis are more likely to affect the hypothalamus. A specific injury can cause siadh, panhypopituitarism, and other severe defects. In some cases these may be transient, but may persist and need replacement therapy. Hormone levels can be measured to look for hypothalamus injury. The exact cause for the damage may not be able to be determined.