Examining the Evidence
Chronic pelvic pain: 11 critical questions about causes and care
An expert explores anatomic and mechanistic bases of chronic pelvic pain in women to clarify optimal diagnosis, management, and treatment
IN THIS ARTICLE
Dr. Howard is a consultant to Ortho Women’s Health & Urology and a speaker for Abbott Pharmaceutical.
CASE: Multisystem involvement
makes diagnosis and treatment thorny
Sara B. is a 26-year-old gravida 4, para 3, abortus 1 who visits your office to be evaluated for chronic pelvic pain. She says her pain is most intense before and during her period and with intercourse. It is located primarily in her abdominopelvic area, but radiates to her lower extremities and lumbosacral back. It appears to be related to bowel function and meets Rome II criteria for irritable bowel syndrome (criteria developed by a panel of experts convened by the Rome Foundation).
Sara B. reports that she voids at least 20 times a day and once during the night. She has a history of depression, for which she takes sertraline (Zoloft), but no history of physical or sexual abuse. When she underwent laparoscopy more than 1 year ago, endometriosis was diagnosed visually.
Upon physical examination, you identify 13 positive fibromyalgia points, moderate tenderness of the posterior levator ani muscles, severe tenderness of the bladder, and moderate tenderness of the uterine fundus. You also find moderate tenderness in the adnexa and uterosacral ligaments bilaterally. Your tentative diagnosis: endometriosis, interstitial cystitis, fibromyalgia, and irritable bowel syndrome.
How do you confirm the diagnosis? And what treatment should you offer to her?
Chronic pelvic pain (CPP) is anything but simple. Sara B.’s case illustrates some of the complexity involved in the diagnostic evaluation and treatment of this disorder. Very rarely is the pain localized to one organ or system. More commonly, it involves multiple organs or anatomic areas within the pelvic region.
To confirm the diagnosis in Sara’s case, the next step would be a potassium chloride sensitivity test for interstitial cystitis. I would also start her on desipramine for fibromyalgia, and perform laparoscopy and cystoscopy with hydrodistention to explore the diagnosis further.
In Sara’s case, let’s assume that the repeat laparoscopy reveals glomerulations of the bladder but no recurrent endometriosis. I would administer oral pentosan polysulfate sodium and instill heparin and lidocaine in her bladder to improve her voiding pattern significantly (to the range of four to six times a day without nocturia). I would also prescribe continuous oral contraceptives to suppress her menses and alleviate some of her pain. In addition, I would be interested to see what a transjugular pelvic venogram would reveal. If it were to suggest severe pelvic congestion syndrome, I might perform embolization of both ovarian veins to provide additional relief.
Clearly, when confronted with a case as intricate as Sara’s, there are many ways to organize your thinking about the potential diagnoses that may cause or contribute to CPP. This article focuses on anatomic and mechanistic bases for evaluation of this disorder as a means of tailoring treatment appropriately. It explores these topics by addressing 11 critical questions, ranging from how pain is described to what to do about it.
1. How is pain defined?
Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage.1
Pain is defined in this way to make it clear that it is not just a sensory experience, but both a sensory and emotional experience. This means that the pain is always subjective and is not the same in all individuals—nor does it remain the same in the same person.
Individuals base their descriptions of pain on their unique prior experience of it. Many people report pain in the absence of tissue damage or any likely pathophysiologic cause, often for psychological reasons. If they regard their experience as pain and report it as they would pain caused by tissue damage, it should be accepted as pain. In defining pain, it is best to deliberately avoid tying pain to the stimulus.
What about CPP? There is no generally accepted definition. The American College of Obstetricians and Gynecologists (ACOG) defines it as noncyclic pain of at least 6 months’ duration that localizes to the anatomic pelvis, lumbosacral back, buttocks, or anterior abdominal wall at or below the umbilicus and that is severe enough to cause functional disability or lead to medical care.2
2. How many women suffer chronic pelvic pain?
Chronic pelvic pain is more common than is generally recognized. Here are some estimates:
- A US study conducted by the Gallup organization found that 15% of women 18 to 50 years old had CPP3
- A survey of women in family medicine and ObGyn offices found that 39% had CPP, although only 8% reported having it more often than “sometimes”4
- The Oxfordshire Women’s Health Study, a postal questionnaire survey of a random sample of women 18 to 49 years old in the general UK population, found a prevalence of 24%5
- A primary-care database in a UK study of women 15 to 73 years old found a prevalence of 38 cases for every 1,000 women. (The database contained annualized data that excluded women who had only dysmenorrhea or dyspareunia.) Although the study likely underestimated the prevalence of CPP, the finding does make it possible to compare prevalences in the same population: asthma (37/1,000), back pain (41/1,000), and migraine (21/1,000).6
3. What are the main types of pain involved?
They are nociceptive, inflammatory, and neuropathic pain.
Nociceptive pain occurs in response to a noxious stimulus that alerts the organism to impending tissue injury. One way to think of nociceptive pain is as “normal” or physiologic pain (FIGURE).
Acute pelvic pain is usually nociceptive in origin. CPP is usually not solely nociceptive in origin. It often involves inflammatory or neuropathic pain, or both (TABLE 1).
Inflammatory pain arises in response to tissue injury and the resulting inflammatory process. In some cases, the inflammatory response is actually a source of tissue injury (e.g., rheumatoid arthritis). Inflammatory pain may be an important mechanism in both acute and chronic pelvic pain.
Neuropathic pain is produced by damage to or dysfunction of neurons in the peripheral or central nervous system. It is not physiologic and is often a significant mechanism in the generation of CPP.
An understanding of inflammatory and neuropathic mechanisms is not esoteric, but has clinical significance.
FIGURE Noxious stimulus is often the trigger in acute and chronic pain
Nociceptive pain is a response to a noxious stimulus, alerting the organism to impending tissue injury. Four fundamental processes are involved in nociceptive pain: transduction, in which the stimulus is converted to a biochemical signal; transmission, in which the signal is transported from the peripheral nervous system to the dorsal ganglion and central nervous system; modulation, in which the intensity of the signal is increased or decreased; and perception, in which the organism experiences the pain.TABLE 1
Anatomic and mechanistic classification of pain
My experience caring for patients who have CPP suggests that chronic pain is a disease, whereas acute pain is a symptom. This concept is controversial in gynecology, and CPP is often labeled as only a symptom, not a diagnosis.7 The search for one underlying disease means that the woman who has CPP frequently undergoes multiple surgical and other invasive procedures, often with incomplete or insignificant diagnoses and responses.
The assumption that CPP is always due to a specific pathologic process in somatic structures or viscera (nociceptive pain) excludes the possibility that CPP can be caused by prolonged or permanent dysfunction of the peripheral or central nervous system, or both (neuropathic pain), or by psychological mechanisms (central pain). Clinical knowledge lags behind basic science in this area and is not at all concrete.
Our ability to accurately diagnose neuropathic or inflammatory pain leaves room for improvement.
5. Is chronic pelvic pain a gynecologic disorder?
Gynecologists have traditionally thought of CPP as either gynecologic or nongynecologic in origin, but this framework has very limited clinical utility. An anatomic and mechanistic classification (TABLE 1) represents a far richer strategic approach to the diagnostic evaluation of CPP, allowing more comprehensive and effective treatment.
6. What distinguishes visceral from somatic pain?
In addition to recognizing the importance of nociceptive, inflammatory, and neuropathic mechanisms in the generation of CPP, it is useful to classify potential causes anatomically (TABLE 1). In the broadest anatomic categories, pain may be central or peripheral, or both. Central pain can be psychogenic or neurogenic, and peripheral pain can be visceral or somatic.
Visceral sources of CPP include the reproductive, genitourinary, and gastrointestinal (GI) tracts. Mechanistically, as has been discussed, visceral pain can be neuropathic, inflammatory, or nociceptive.
Potential somatic sources of CPP are myofascial, skeletal, and cutaneous. Mechanisms leading to somatic CPP can be neuropathic, inflammatory, or nociceptive.
Somatic pain is better understood than visceral pain, but knowledge about the latter has been expanding rapidly. Several characteristics distinguish visceral pain:
- Not all viscera generate pain, possibly owing to a lack of sensory receptors or appropriate nociceptive stimulus
- Visceral pain is not always linked to injury and, therefore, may be functional
- Visceral pain frequently results in somatic referral of pain, possibly due to central convergence of visceral and somatic afferents
- Visceral pain tends to be diffuse or poorly localized, probably because of the low concentration of nociceptive afferents within viscera (only 2% to 10% of total afferents to the spinal cord originate from visceral nociceptors).8
It is not clear whether there are visceral neurons dedicated solely to nociception; it appears that viscera utilize sympathetic and parasympathetic neurons as nociceptors. It also is important to note that the stimuli that activate somatic nociceptors—cutting, crushing, and burning, for example—do not generally cause visceral pain. Visceral nociceptive pain is generated in response to:
- distention of a viscous or organ capsule
- spasm of visceral muscular fibers
- ischemia from vascular disturbances
- traction on mesentery.
Another characteristic that distinguishes visceral from somatic nociception: Visceral nociception utilizes a dorsal midline pathway within the central nervous system, in addition to the lateral spinothalamic tract pathway utilized by somatic nociception.
Although this anatomic and mechanistic classification is clinically useful in the diagnostic evaluation of CPP, it is an oversimplification. Most patients—like Sara B., described in the opening case—have multiple anatomic and mechanistic causes of their pain.
7. What are the primary visceral causes of chronic pelvic pain?
A limited number of visceral and somatic diagnoses are backed by level-A evidence as having a causal relationship with CPP (TABLE 2). A few are discussed here.
Disorders that may cause CPP or make it worse*
* Disorders with Level-A evidence, i.e., good and consistent scientific evidence of a causal relationship to CPP
Disorders of the reproductive tract
Endometriosis is the most common gynecologic diagnosis in women who have CPP. There is significant epidemiologic evidence that endometriosis causes CPP. There is also strong evidence that endometriosis is a risk factor for CPP.
For example, human and animal experimental data suggest that women who have endometriosis have more episodes of urinary calculosis—and more severe pain—than women who do not have endometriosis.9,10 They also are more likely to report vaginal pain than are women who do not have endometriosis, and that vaginal pain is more likely to be severe.
Such viscerovisceral interactions may play a significant role in CPP in women and may explain why some women who have a history of endometriosis have persistent pelvic pain after their endometriosis is gone, or even appear to develop other pain syndromes, such as interstitial cystitis.11
Our introductory case illustrates these concepts. Sara B.’s history is classic for endometriosis-associated pelvic pain; that was her original diagnosis. Although her pelvic pain recurred and persisted, a repeat laparoscopy found no endometriosis—but it did reveal evidence of interstitial cystitis and painful bladder syndrome (IC/PBS). Could Sara’s current pain be neuropathic or inflammatory?