Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with a doctor.
Without the ability to examine and obtain a history, I can not tell you what the exact cause of the symptoms is. However I will try to provide you with some useful information.
It is difficult to answer this question without further information. Neck stiffness can be a symptom of a serious condition such as meningitis. It is good your husband was evaluated. Additionally, I would be concerned about the blood vessels in the neck if there has been any neck injury, chiropractor manipulation, etc. What was your husband doing at the time of the neck stiffness or before the neck stiffness? Is the neck stiffness bilateral or one-sided? Has your husband had an MRI of the cervical spine? Does your husband have pain radiating down one arm? These questions are important to address.
After the more serious causes of neck stiffness have been ruled out, your husband may benefit from physical therapy/muscle stretching techniques. Other options include massage, aqua therapy, acupuncture, or even chiropractor/osteopathic manipulation (if indicated).
Before starting an exercise routine, you should be evaluated by your physician if you have cardiac or neurological risk factors.
Lastly, if the muscle spasms are considered to be a form of dystonia, a referral to a movement disorder specialist would be appropriate.
Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.
Also, just a quick history in case all of this is related. He just got over a "back injury" (although there is really no known cause as to why this began either). He began getting severe sacroiliac joint pain about a month ago. We treated this with a chiropractor and massage therapy. The same pain (perhaps worse) happened in March of this year. In August, he lost the side to side motion in his right wrist and a doctor told him he had De Quervain's tenosynovitis (this is when we went to get a blood test for rheumatoid arthritis). He's had swelling joints and joint pain in his fingers and hands over the last couple of years. Also, in October of 2010 he was diagnosed with sinus tarsi syndrome in his left foot (although the symptoms have completely disappeared since he stopped going down huge amounts of stairs from his previous job). When he was 18 years old, he slipped a disc in his lower back (he used to build and move stair cases).