CHAPTER 11 Chronic Abdominal Pain

Definition and Clinical Approach 163

Abdominal Wall Pain 164

Anterior Cutaneous Nerve Entrapment and Myofascial Pain Syndromes 164

Slipping Rib Syndrome 165

Thoracic Nerve Radiculopathy 165

Functional Abdominal Pain Syndrome 165

Epidemiology 165

Pathophysiology 165

Clinical Features 168

Diagnosis and Differential Diagnosis 169

Treatment 169

Role of Laparoscopy with Lysis of Adhesions 170

The evaluation of any patient with a complaint of abdominal pain is challenging. Abdominal pain can be benign and self-limited or a harbinger of a serious life-threatening disease (see Chapter 10). Chronic abdominal pain poses a particularly challenging clinical problem. Not only is the management of chronic abdominal pain a frequently daunting task, but also the possibility of overlooking a structural or organic disorder is always a concern. Many disorders discussed elsewhere in this text can produce chronic abdominal pain (Table 11-1). Many of these diagnoses require careful consideration and clinical interrogation, in addition to appropriate diagnostic testing, to discern whether the entity is indeed the cause of the patient’s pain. Diagnosis of a functional gastrointestinal disorder is generally considered once potential causes of organic chronic abdominal pain have been confidently excluded. Although the causes of chronic abdominal pain are varied, the pathophysiologic pathways that produce chronic pain are common to many of them. This chapter focuses on the neuromuscular causes of chronic abdominal pain and the functional abdominal pain syndrome (FAPS). FAPS serves as a model to illustrate many of the complex issues involved in caring for patients with chronic abdominal pain.

Table 11-1 Differential Diagnosis of Chronic or Recurrent Abdominal Pain

Structural (or Organic) Disorders

Inflammatory

Appendicitis (Chapter 116)

Celiac disease (Chapter 104)

Eosinophilic gastroenteritis (Chapter 27)

Fibrosing mesenteritis (mesenteric panniculitis) (Chapter 37)

Inflammatory bowel diseases (Chapters 111 and 112)

Pelvic inflammatory diseases

Primary sclerosing cholangitis (Chapter 68)

Vascular

Celiac artery syndrome (Chapter 36)

Mesenteric ischemia (Chapter 114)

Superior mesenteric artery syndrome (Chapter 14)

Metabolic

Diabetic neuropathy

Familial Mediterranean fever (Chapter 35)

Hereditary angioedema

Porphyria (Chapter 76)

Neuromuscular

Anterior cutaneous nerve entrapment syndrome

Myofascial pain syndrome

Slipping rib syndrome

Thoracic nerve radiculopathy

Other

Abdominal adhesions (Chapter 119)

Abdominal neoplasms (Chapters 29–32, 46, 54, 60, 69, 94, 121–123)

Anaphylaxis (Chapter 9)

Chronic pancreatitis (Chapter 59)

Endometriosis (Chapter 124)

Gallstones (Chapter 65)

Hernias (Chapter 24)

Intestinal malrotation (Chapter 96)

Intestinal obstruction (Chapter 119)

Lactose intolerance (Chapter 101)

Peptic ulcer disease (Chapter 52)

Small intestinal and pelvic lipomatosis (Chapter 37)

Functional Gastrointestinal Disorders

Biliary pain (gallbladder or sphincter of Oddi dysfunction) (Chapter 63)

Functional abdominal pain syndrome

Functional (nonulcer) dyspepsia (Chapter 13)

Gastroparesis (Chapter 48)

Irritable bowel syndrome (Chapter 118)

Levator ani syndrome (Chapter 125)

DEFINITION AND CLINICAL APPROACH

Abdominal pain is considered chronic when it has been occurring constantly or intermittently over at least six months. Abdominal pain is considered acute when it has been occurring for several days and subacute when it has been occurring more than several days but less than 6 months. These arbitrary definitions are often helpful when formulating a differential diagnosis. The clinician initially must adopt a broad-based approach, which necessarily becomes more focused as the evaluation ensues. Importantly, although typical patterns of presentation are useful to remember, some patients, especially immunosuppressed and older persons, may present with atypical features.

As for acute abdominal pain (see Chapter 10), the initial step in evaluating a patient with chronic abdominal pain is to elicit a detailed history from the patient. The chronology of the pain, including its abruptness of onset and duration, and its location and possible radiation should be determined. Visceral pain emanating from the digestive tract is perceived in the midline, because of the relatively symmetrical bilateral innervation of the organs, but is diffuse and poorly localized.¹ Referred pain is ordinarily located in the cutaneous dermatomes that share the same spinal cord level as the affected visceral inputs.² The patient should be questioned about the intensity and character of the pain, with the understanding that these parameters are subjective. The patient’s perception of precipitating, exacerbating, or mitigating factors may be useful when diagnostic possibilities are considered.

When initially attempting to determine whether the patient’s pain is caused by an organic or functional process, the clinician should search for clues in the patient’s history and physical examination that support or refute the diagnosis of a progressive, serious, chronic underlying illness. Such features in the history include fever, night sweats, appetite change, weight loss, and nocturnal awakening.

A complete physical examination is indicated to look for evidence of a systemic disease. The abdominal examination should use a combination of inspection, auscultation, percussion, and palpation. The most critical step for a patient with an acute exacerbation of chronic abdominal pain is to ascertain promptly whether a surgical abdomen is present (see Chapter 10). Although most causes of chronic abdominal pain do not require immediate surgical treatment, a complication related to a disease process ordinarily associated with chronic abdominal pain may present acutely (e.g., intestinal perforation in a patient with inflammatory bowel disease). Furthermore, a patient who has experienced chronic abdominal pain may present with acute pain related to another disease process (e.g., acute mesenteric ischemia in a patient with underlying irritable bowel syndrome [IBS]). The abdomen should be auscultated to detect an abdominal bruit, because the presence of a bruit may suggest chronic mesenteric ischemia (intestinal angina). Abdominal palpation for the presence of organomegaly, masses, and ascites and examination for hernias are particularly pertinent. Other physical findings that suggest an underlying organic illness include signs of malnutrition (e.g., muscle wasting or edema), vitamin deficiencies, or extraintestinal processes (e.g., arthropathy or skin changes). Although not entirely specific, the closed eyes sign is often seen in patients with FAPS (see later). Similarly, Carnett’s sign and the hover sign (described later) may be seen in persons with abdominal wall pain.

The laboratory evaluation can be helpful, but the clinician must first distill pertinent facets of the history and physical examination to focus the laboratory assessment. Injudicious use of laboratory testing is costly and can confuse the clinical picture and even lead to complications. It is worth emphasizing that an abnormal laboratory test result does not necessarily prove causality in relation to a patient’s chronic pain syndrome. The clinician must exercise the utmost discretion when ordering and interpreting the results of laboratory tests.

Endoscopic and imaging studies have important roles in diagnosing and excluding many causes of chronic abdominal pain. Upper endoscopy and colonoscopy, as well as capsule endoscopy, may be indicated in selected cases. Available imaging investigations include barium and radionuclide studies, ultrasonography, computed tomography, magnetic resonance imaging, positron emission tomography (PET), and conventional angiography. The indications for each of these radiologic investigations differ, as do their potential to clarify an individual clinical situation. Endoscopic and radiologic testing in specific disorders is discussed in detail elsewhere in this text.

ABDOMINAL WALL PAIN

ANTERIOR CUTANEOUS NERVE ENTRAPMENT AND MYOFASCIAL PAIN SYNDROMES

Anterior cutaneous nerve entrapment syndrome (ACNES) and myofascial pain syndrome (MFPS) are common causes of chronic abdominal wall pain. These syndromes share clinical, diagnostic, and treatment characteristics. The importance of recognizing these syndromes rests in providing the patient with an accurate diagnosis and effective treatment, as well as avoiding further expensive investigation and unnecessary surgical intervention. The abdominal wall should be suspected as the cause of symptoms when there is a complaint of chronic and unremitting abdominal pain that is unrelated to eating or bowel function but clearly related to movement.

Although ACNES was initially described in the 1970s, it remains a frequently overlooked cause of chronic abdominal pain.^3,⁴ In ACNES, the pain is believed to occur when there is entrapment of a cutaneous branch of a sensory nerve that is derived from a neurovascular bundle emanating from spinal levels T7 to T12. The nerve entrapment may be related to pressure from an intra- or extra-abdominal lesion or to another localized process, such as fibrosis or edema. Pain emanating from the abdominal wall is discrete and localized, in contrast to pain originating from an intra-abdominal source, which is diffuse and poorly localized. Patients usually point to the location of their pain with one finger, and the examiner can often localize the area of maximal tenderness to a region less than 2 cm in diameter. During physical examination, the patient often guards the affected area from the examiner’s hands (hover sign).⁵ Patients often note that activities associated with tightening of the abdominal musculature are associated with an exacerbation of pain and, during physical examination, the clinician will note increased localized tenderness to palpation when the patient tenses the abdominal muscles (Carnett’s sign).⁶ In contrast, an increase in tenderness during relaxation of the abdominal musculature suggests an intra-abdominal source of pain.

In MFPS, pain emanates from myofascial trigger points in skeletal muscle.⁷ Causative factors include musculoskeletal trauma, vertebral column disease, intervertebral disc disease, osteoarthritis, overuse, psychological distress, and relative immobility. The exact pathophysiology of pain in MFPS remains unclear. Chronic abdominal wall pain may occur in patients with MFPS. Pain may be referred from another site, and the identification of trigger points (including those remote from the site of pain) is a useful physical finding. When attempting to identify a trigger point, the examiner uses a single finger to palpate a tender area. This is most often located in the central portion of a muscle belly, which may feel indurated or taut to palpation, and elicits a jump sign.⁸ This finding refers to a patient’s response by wincing, jerking away, or crying out as the myofascial trigger point is detected. Less commonly, trigger points may be located at sites such as the xiphoid process, costochondral junctions, or ligamentous and tendinous insertions.

Treatment of ACNES and MFPS, when successful, not only improves symptoms, but also confirms the diagnosis.^9,¹⁰ The treatment strategy depends on the severity of the symptoms. With mild and intermittent symptoms that are reproducibly precipitated by certain movements, simple reassurance and a recommendation to avoid such movements may suffice. Non-narcotic analgesics, nonsteroidal anti-inflammatory drugs (NSAIDs), and application of heat can be used during exacerbations. Physical therapy may be beneficial, although no randomized studies have supported this treatment modality. For severe and persistent symptoms, injection therapy with a local anesthetic, with or without a glucocorticoid, is recommended.⁹^–¹¹ In one study of 136 patients in whom the history and physical examination suggested abdominal wall pain, and in whom benefit was noted with injection therapy, the diagnosis remained unchanged after a mean follow-up of four years in 97% of cases.¹² In carefully selected patients with symptoms refractory to injection therapy, a prospective nonrandomized investigation has suggested that diagnostic laparoscopy with open exploration of abdominal trigger points may be beneficial.¹³ In this study, after intra-abdominal adhesions in close proximity to trigger points were lysed, subcutaneous nerve resection was performed. After a median postoperative follow-up of 37 months, 23 of 24 patients (96%) believed that this approach was beneficial in managing their previously intractable pain.

SLIPPING RIB SYNDROME

The slipping rib syndrome (SRS), which was described initially in the early 20th century,^14,¹⁵ is an uncommonly recognized cause of chronic lower chest and upper abdominal pain. SRS ordinarily causes unilateral, sharp, often lancinating pain in the subcostal region. The acute pain may be followed by a more protracted aching sensation. The syndrome is associated with hypermobility of the costal cartilage at the anterior end of a false rib (rib 8, 9, or 10), with slipping of the affected rib behind the superior adjacent rib during contraction of the abdominal musculature. This slipping causes pain by a variety of potential mechanisms, including costal nerve impingement and localized tissue inflammation. The key to diagnosis is clinical awareness of the syndrome, in conjunction with use of the hooking maneuver; the clinician hooks his or her examining fingers underneath the patient’s lowest rib and, as the rib is moved anteriorly, the pain is reproduced and an audible pop or click is often heard.¹⁶ Conservative therapeutic measures often suffice but, on occasion, costochondral nerve blockade, response to which supports the diagnosis, or even surgical rib resection is required.¹⁷

THORACIC NERVE RADICULOPATHY

Disease related to thoracic nerve roots T7 through T12 may be responsible for abdominal pain. The disease processes that may cause this problem include neuropathy related to back and spine disorders, diabetes mellitus, and herpes zoster infection.^18,¹⁹ Obtaining a complete history and performing a careful physical examination of the patient, with attention to the possibility of a systemic disease and abnormal neurologic and dermatologic findings, should lead to the correct diagnosis in most instances. Treatment depends on the specific underlying disease process.

FUNCTIONAL ABDOMINAL PAIN SYNDROME

FAPS is a distinct medical disorder. Evidence suggests that the syndrome relates to central nervous system (CNS) amplification of normal regulatory visceral signals, rather than functional abnormalities in the gastrointestinal tract.^20,²¹ The disorder is characterized by continuous, almost continuous, or at least frequently recurrent abdominal pain that is poorly related to bowel habits and often not well localized. FAPS is properly understood as abnormal perception of normal (regulatory) bowel function rather than a motility disorder. The syndrome appears to be closely related to alterations in endogenous pain modulation systems, including dysfunction of descending and cortical pain modulation circuits.²¹ The Rome III diagnostic criteria for FAPS are shown in Table 11-2.^20,²¹ Studies that included patients who meet diagnostic criteria for FAPS have revealed that only rarely is an organic cause of chronic abdominal pain found during long-term follow-up.^22,²³

Table 11-2 Rome III Criteria for Functional Abdominal Pain Syndrome *

Must include all the following:

1. Continuous or almost continuous abdominal pain

2. No or only occasional relationship of pain with physiologic events (e.g., eating, defecation, menses)

3. Some loss of daily functioning

4. Pain is not feigned (e.g., no malingering)

5. Insufficient symptoms to meet criteria for another functional gastrointestinal disorder that would explain the pain

* Criteria fulfilled for the past three months with symptom onset at least six months prior to diagnosis.

FAPS is commonly associated with other unpleasant somatic symptoms, and, when it persists or dominates the patient’s life, it usually is associated with chronic pain behaviors and comorbid psychological disturbances.²⁴ Patients with FAPS typically define their illness as medical, and their symptoms tend to be more severe and associated with greater functional impairment than those of patients with IBS.²⁴ Psychological disturbances, if present, must be considered as comorbid features of FAPS rather than as part of a primarily psychiatric problem.²⁵ When compared with patients who have chronic back pain, those with chronic abdominal pain report significantly better physical functioning, yet their overall perception of health is significantly worse.²⁶

EPIDEMIOLOGY

Although the epidemiology of FAPS is incompletely known, in the U.S. Householder Survey of Functional Gastrointestinal Disorders, FAPS was estimated to be present in 2% of the sample and was less frequent than IBS (9%).²⁷ A female predominance was noted (F:M = 1.5). Patients with FAPS missed more work days because of illness and had more physician visits than those without abdominal symptoms. A substantial proportion of patients are referred to gastroenterology practices and medical centers; they have a disproportionate number of health care visits and often undergo numerous diagnostic procedures and treatments.