Complication

The act or process of complicating; the state of being complicated; intricate or confused relation of parts; entanglement; complexity.

A disease or diseases, or adventitious circumstances or conditions, coexistent with and modifying a primary disease, but not necessarily connected with it.

any disease or disorder that occurs during the course of (or because of) another disease; "bed sores are a common complication in cases of paralysis"

puzzling complexity