Protean in standard English has the meaning of something that appears in many different forms. In the same vein, in radiological usage it is used to describe a condition which can assume multiple different guises. One of its classic uses is for the imaging appearance of osteomyelitis which can look like virtually anything.
It is derived from a name (see below) and therefore may be capitalized or non-capitalized.
History and etymology
From the Ancient Greek name Proteus, a god of the sea who was a shapeshifter, and therefore could take on an infinite variety of appearances .