Assessment of Central Pain in the Peripartum Period

Chronic pain is common. Up to 10% of the Population has been estimated to suffer from chronic pain and up to 5% of the female population has been estimated to suffer from widespread, chronic pain and tenderness, thus fulfilling American College of Rheumatology (ACR) criteria for classification of fibromyalgia syndrome (FMS)(1;2). FMS is considered to represent a prototype of chronic pain which is mediated by the central nervous system, i.e. a condition in which chronic pain is the result of augmented pain processing (and diminished pain - inhibition) within the Central Nercous System (CNS) circuitry (3). Clinical characteristics which are suggestive of the presence of central, versus peripheral (nociceptive) or neuropathic pain, are a lifetime history of pain conditions, a diffuse, non- anatomical distribution of pain, a family history of chronic pain and the co-existence of additional "functional" symptoms such as chronic fatigue, disturbed sleep, irritable bowel etc.

The current paradigms accepted for the pathogenesis of central pain involve an imbalance of multiple neurotransmitters in the CNS, some inhibitory (e.g. serotonin, norepinephrine) others facilitatory (e.g. substance P) which govern the process of spinal pain transmission. Additional processing takes place at higher centers, such as the amygdala and thalamus (4).

FMS is characterized by the presence of both allodynia and hyperalgesia. In addition, medications which have been shown to be effective in FMS and similar conditions are different from those effective in acute pain or in other chronic pain conditions not characterized as central (e.g. malignancy - associated pain). Thus, opioids and Non Steroidal Anti-Inflammatory Drugs (NSAIDS) are relatively ineffective for the treatment of central pain (the former may even cause paradoxical hyperalgesia) (5) while medications which increase levels of norepinephrine and serotonin (NSRIs) are often effective. FMS is also characterized by disturbances of the autonomic nervous system such as orthostatic intolerance, postural tachycardia etc.(6) The effect of these conditions during gestation and post partum periods is not well known.

Parturition is a complex process which involves multiple endocrine and physiological changes within a short period of time. Severe pain is an important attribute of this natural process. The processes of labor, delivery and also the peripartum period are characterized by acute shifts in volume, loss of blood and additional forms of physiological stress and emotional distress.

The purpose of the current study is to evaluate the impact of chronic central pain on the process of parturition. Our hypothesis is, that women demonstrating signs, symptoms and a history of central pain, before the onset of active labor, will differ from women not demonstrating such traits; these women may require earlier higher does of analgesia, and may demonstrate increased hemodynamic lability during labor and delivery.