What type of lighting are you using?
What are your Temps?
Do you use any supplements?
Your problem is not Hypotheremia , but Metabolic Bone disease. An Iguana cannot Metabolize the Calcium unless you are using a UVB bulb which simulates sunlight. The first sign of MBD is twitching and shaking. This Ig needs to get under a UVB light or into some direct sunlight asap. This will help. This is the type of bulb you should be using.
The Temps should be about 80*-90*F . This is another link that will help you with the care. Joan