Nighttime pain may present as an important symptom several ways. There are conditions in which pain or discomfort is felt essentially only at night; these are fairly few but noteworthy. Then, there are those conditions which seem to be exacerbated at nighttime. The role of "nighttime" in these conditions exacerbation needs to be explored. Finally, there are those conditions which are not necessarily worse at night, although perhaps more apparent for their lack of disappearance, in other words, in most conditions one would expect relief at the end of the day when one finally climbs into bed. Lack of improvement of symptoms overnight may also be an important symptom.

Factors that may cause increased nocturnal pain.

Factors which may result in emergence of or increase in pain at night can be grouped as hormonal and mechanical. The effect of hormonal fluctuations on our physical biochemistry and pain perception is very poorly understood. We know, for example, that fluctuation in glucocorticoids results in early evening fevers in many infections or inflammatory conditions. It is possible that lower glucocorticoid levels in the evening allow emergence or exacerbation of pain at night, just as glucocorticoids can be used to reduce pain by reducing inflammation in rheumatic conditions. This stands to reason, but further investigation needs to be done. The role of the pineal gland in diurnal variations, the relationship of "jet lag" to changes seen in chronic fatigue, as well as the fatigue associated with fibromyalgia and other rheumatic conditions, needs further research. What about the effect of variations in female hormones on a cyclical basis and daily variations in estrogen and progesterone? These hormones almost definitely play a role in conditions involving pain. Estrogens are also known to play a role in promoting better sleep patterns.

Better understood are the roles of mechanical factors in causing or exacerbating pain. Being supine or prone (i.e., in extension) can compress posterior structures and increases loading of posterior elements of the spine. Arterial flow to the lower extremities is impeded and venous return may be enhanced, resulting in central pooling and increased central edema. Other mechanical factors include compression of structures in the neck and shoulders in certain positions which may result in increased pain at night as well.

Pain only nocturnal

Several conditions may present with pain felt only at night. Cervicalosteoarthritis and carpal tunnel syndrome, although normally felt during the day as well, may present with pain which is only nocturnal. This is especially true with mild carpal tunnel syndrome if there is a component of edema or fluid retention. Cervical osteoarthritis is often exacerbated by positioning at night, and additional support for the posterior neck may be necessary in addition to the regular pillow. Alternatively, many patients receive benefit from cervical pillows which distribute the weight bearing of the neck and head more evenly.

There are patients who have low back pain or a "heavy" sensation in their legs only at night. This has been referred to as "Ondine’s curse", and is the result of borderline or mild lumbar spinal stenosis concomitant with incipient congestive heart failure. These patients have venous pooling which results in increased venous engorgement in their epidural veins; this occurs primarily at night when lying down. This results in reduced effective lumbar canal diameter in an already compromised canal, precipitating the symptoms of spinal stenosis, interestingly, in these patients, a diuretic may be the treatment of choice.

Another condition which occurs solely at night is nocturnal paroxysmal myoclonus, or "restless leg syndrome". This condition is poorly understood, but is characterized by restlessness, as well as muscle cramping and involuntary contraction of muscles of the legs. This is a painful condition which may interfere with sleep and precipitate other painful conditions such as fibromyalgia; once diagnosed, it responds fairly well to medications, splinting, and exercise, its origin is poorly understood.