The most important illnesses to mention that may cause stiff neck and fever are meningitis and encephalitis because these are very dangerous. Other conditions that could result in the two symptoms are mononucleosis, tetanus, and subarachnoid hemorrhage. Certain arthritic disorders like ankylosing spondylitis, Felty syndrome, and osteoarthritis are sometimes associated with stiff neck and fever. Alternately, the two symptoms might be unrelated to each other or not indicative of serious disease.
The reason why stiff neck and fever are viewed as concerning is principally due to the fact that they are the most recognizable symptoms of meningitis and encephalitis. Especially in meningitis, the neck is often suddenly very stiff and people are unable to touch the chin to the chest. A fever is likely to be high, too. In encephalitis, the neck may still move with greater ease, but the stiffness is often painful. Both conditions usually feature a significant headache, also.
The stiff neck of mononucleosis is described differently. It’s usually due to extremely swollen glands, and most patients also have very bad sore throats. Fever may be mild to severe, depending on the individual, and this disease is not usually life-threatening. Tetanus, in contrast, can be more serious, though it is rare. It can cause spasms in the jaw, neck, chest, and stomach. People with regular tetanus inoculations are unlikely to contract this illness.
A subarachnoid hemorrhage differs from tetanus or mono because it is not caused by viral or bacterial infections. Instead, it is typically caused by aneurysms — abnormally widened arteries in the brain — that burst, resulting in bleeding. Alternately, head injuries may result in bleeding in the brain. When this hemorrhaging begins, people may experience a still neck and fever, and this condition is also associated with headaches.
In arthritic conditions, deteriorating joints may cause progressive stiffness in the neck. Arthritis that is autoimmune in origin may raise temperature, too. In these illnesses, the symptoms of a stiff neck and fever might both be mild, but over time, arthritis in the neck could worsen. Autoimmune disorders of many other kinds could feature pain in the neck and mysterious fevers. When people have compromised immune systems, they are also more vulnerable to encephalitis and meningitis, so these symptoms should always be taken seriously.
It is also possible for minor viral infections to result in slight neck stiffness, accompanied by other aches, and a small fever. Alternately, the two conditions don’t have to be related. Someone with a cold could sleep on too many pillows and wake up with a stiff neck and fever. Still, these symptoms should never be dismissed given their potential gravity, and performing the chin to chest move is a good home test to determine if meningitis is a concern. This self-exam cannot rule out encephalitis or other serious causal factors of these symptoms, though, so a medical exam is still advised.