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Evaluation and Management of Abdominal Myofascial Pain Syndrome

James K. C. Wang, MD; James G. Gebhardt, MD

Common Clinical Scenario: A 32-year-old woman presents with a 5-year history of right-sided pelvic pain and dyspareunia. She has seen several ObGyn physicians and undergone 2 laparoscopies for presumed endometriosis, but no lesions were identified. Her current ObGyn recommended a hysterectomy. The patient requests a second opinion.

Chronic pelvic pain (CPP) is a common condition affecting more than 9 million women in the United States.1 While it accounts for more than 10% of gynecologic referrals, it remains a difficult disorder to diagnose and treat.2 More than 40% of laparoscopies and 18% of hysterectomies are performed for CPP.3 Reproductive organs account for only 20% of patients with CPP.4 The musculoskeletal system is an underappreciated source of CPP. With appropriate history and physical exam, CPP of this origin can often be easily diagnosed and treated.

CPP of musculoskeletal origin is usually separated into 2 categories: Pain originating from the muscles or fascia of the abdominal wall is referred to as abdominal myofascial pain syndrome (AMPS), whereas pain originating from the pelvic muscles or fascia is called myofascial pelvic pain syndrome (MPPS). For this article, we will focus on AMPS.

AMPS is characterized as pain originating from myofascial triggering points (MTrPs) in the abdominal region. In the experience of one group of CPP specialists, about 30% of women with CPP had AMPS.5

AMPS arises from muscular dysfunction from chronic tension, trauma, or inflammation, which results in and stimulates the development of MTrP. Over time, the problem can spread by 2 distinct mechanisms. First, as one area of the muscle becomes tense and overloaded, it increases tension on adjacent areas by a direct, local physical mechanism. Secondly, the chronic pain signals can lead to central nervous system sensitization, leading to pain that is more widespread and more resistant to treatment. By these mechanisms, pain in one part of the abdomen may ultimately result in radiating pain in other parts of the abdomen, the lower back, or perineum. It may result in the development of MPPS.6

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History

Certain features of a detailed history may suggest AMPS. However, the principle of parsimony in diagnosis (Occam’s razor) does not always apply. Diagnosis of AMPS can be complicated by the fact that other conditions that cause CPP, such as painful bladder syndrome/interstitial cystitis, vulvodynia, and endometriosis, are often found as concurrent diagnoses.

AMPS may cause constant or intermittent pain. Distinct from CPP caused by endometriosis, it may be exacerbated by certain postures and physical activity and may radiate to the lower extremities or the back. Patients will often have a history of previous abdominal surgery or back problems. Although AMPS may worsen temporally due to menstrual cycles, it is not limited to them. The pain is generally perceived as deep and visceral and is often described as “ovarian pain.” Urinary tract discomfort, dyspareunia, and vulvar pain are common associated symptoms. A detailed diary describing the pain is invaluable in assessing the patient’s symptoms (Table 1).

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TABLE 1. Features Suggestive of Abdominal Myofascial Pain Syndrome

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Physical Exam

The physical exam should be directed toward isolating the source of pain (Table 2). Scoliosis, lower extremities of unequal length, and neurologic deficits should be noted.

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TABLE 2. Physical Exam for Abdominal Myofascial Pain Syndrome

The neck, spine, and paraspinous musculature should be palpated. Commonly, women with lumbar muscle spasm or vertebral disc disease will exhibit significant pain on palpation of the structures. The pain may radiate from the paraspinous area to the corresponding dermatome on the abdomen and be confused with AMPS.

Carnett’s test can be used to distinguish between pain arising from the abdominal wall and that from a visceral source. With the patient in supine position with legs flexed at the knees and hips, the area of abdominal tenderness is palpated. The patient then performs a partial sit-up. Abdominal wall pain tends to worsen with this maneuver, whereas pain from a visceral etiology tends to decrease.

Women with AMPS will have tenderness of the abdominal wall corresponding to the historical location of their pain. Palpation can distinguish tightened and tender muscle groups and painful nodularities (eg, MTrPs) in the subcutaneous tissues. Areas adjacent to surgical scars should be inspected with particular attention. Gentle palpation of MTrPs will elicit significant pain.

Following standard abdominal palpation, perform single-finger palpation to check for increased muscle tone or spasm, tenderness (manifested by grimace, vocalizations, or the “jump sign”), referred pain patterns, or muscle twitch. Nodular masses may be palpated adjacent to or directly under trigger points.

MTrPs may be mapped by pressing the wooden end of a cotton swab on the abdominal skin surface. By lightly pressing on the nontender areas of the abdomen first, the clinician can determine the appropriate level of pressure, and the patient will know the sensation of the probe. Pressure should be applied in 4-cm intervals in a descending line until reaching the tender area. Trigger points are identified by locating the most tender spots (usually no more than 2 mm in diameter). Direct pressure to a MTrP will cause pain disproportionate to the amount of stimulus. Patients will usually experience a worsening pain, severe aching, or muscle spasm for a period of time immediately after stimulation of trigger points.

The pelvic exam should include palpation of the mons, labia, and perineal muscles. Contrary to usual routine, palpation of the pelvic structures should be performed before the speculum exam. In patients with interstitial cystitis and MPPS, introduction of a speculum can worsen pain symptoms, decreasing the reliability of a subsequent digital exam. With the bladder empty, perform single-digit palpation of the introitus, urethra, and bladder. One should palpate the pelvic musculature to assess for tightening, bands, or trigger points. Identification of pelvic muscle trigger points is suggestive of MPPS.

During the speculum exam, gentle pressure should be applied to the cervix with a scopette to test for cervical motion tenderness. Testing for sexually transmitted infections is recommended. The bimanual exam should be performed gently, checking for uterosacral nodularity or scarring, uterine fixation, and localized tenderness. Alternating pressure between the abdominal hand and the vaginal hand will help distinguish between abdominal wall and visceral pain.

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Treatment

Several therapies are available as treatment for AMPS. The particular combination used will depend on the severity and duration of the condition and the particular features present.

Prescription NSAIDs or COX-2 inhibitors in conjunction with heat and cold packs are first-line medical therapy. Treatment of pain and inflammation can result in a stimulus-free period that reverses the central sensitization associated with an MTrP. The patient can also use a heated compress to the painful area for 10 to 15 minutes, followed by a 15-minute “cool down” period. A cold pack is then applied for 10 to 15 minutes. This treatment is performed 2 to 3 times a day.

Another treatment is the topical 5% lidocaine transdermal patch. Cut to size, the patch is placed directly over trigger points. Patches are changed every 12 hours as needed. Up to 3 full-sized patches (10 x 14 cm) may be used for up to 12 hours in a 24-hour period, but the need to treat such large areas is unlikely. It may take several days for notable effect.

Treatment of MTrPs using injection of local anesthetic is effective. We recommend trigger point injections using 0.5% bupivacaine with a 22- or 25-gauge 1½-in needle and 10-mL syringe. Lidocaine may be used in place of bupivacaine, but it has a significantly shorter duration of action. It is important to obtain informed consent and warn patients that placement of injections will be painful until the onset of anesthetic effect.

MTrPs are mapped, and locations are visually noted or marked with a permanent marker. The skin is then prepped with alcohol or betadine, and the needle is placed into the site of the trigger point. A small wheal is raised in the skin upon insertion, and the needle is then advanced until it reaches the fascia. This level is distinguished by a subtle increase in resistance as the needle tip enters the fascia; a crunching sensation may be felt. After aspirating to ensure the needle is not intravascular, 1 mL of bupivacaine is injected. If tight muscle bands are present, the needle may then be advanced. Following aspiration, 0.5 to 1 mL is then injected into the muscle. The surrounding area, as well as adjacent trigger points, are then injected by partially withdrawing the needle and redirecting it to other hot spots in a “fan” pattern. If tender nodules are palpated in the subcutaneous tissue, 0.5 to 1 mL may be injected directly into the nodule. Multiple distant trigger point sites should be injected at the same time.

Repeat injections can be scheduled as necessary, but we recommend initially at least one week between injections. From our experience, many patients have long-term relief after one injection. Rarely, the pain may become worse after injection.

Contraindications to MTrP injections include anticoagulation or bleeding disorders, local infection, suspected abdominal hernia, and allergy to the anesthetic. Complications include infection, bleeding, hematoma, and vasovagal syncope. Anesthetic toxicity is extremely rare, but the risk should be considered when performing a large number of injections in patients with low body mass index. The maximum dosage of bupivacaine is 2.5 mg/kg. A 0.5% solution contains 5 mg/mL bupivacaine.

Conclusion of clinical scenario above: The patient described the pain as continuous, both sharp and aching, sometimes radiating down her right thigh. It was worsened by certain movements, intercourse, and the onset of her periods. She denied pain with urination or urinary frequency. Her exam revealed normal posture, no tenderness of the back, and a nontender urethra and bladder. On bimanual exam, the uterus was of normal size, and she was exquisitely tender in the right adnexal area. However, when pressure was released with the abdominal hand, the pain resolved. Abdominal exam with a cotton swab was notable for tenderness and trigger points in the right lower quadrant. When trigger points were pressed, the patient experienced severe pain that radiated down the right thigh. The patient was treated with MTrP injections of 0.5% bupivacaine, and she experienced pain relief for one week. Subsequent injections resulted in complete resolution of her pain symptoms. As this case demonstrates, AMPS is a commonly underrecognized cause of CPP. Simple treatment strategies require no special equipment or training and are effective in the treatment of uncomplicated AMPS.

Dr Wang is on the speakers bureau for Novartis, and he is a trainer for Organon/Schering-Plough. Dr Gebhardt reports no actual or potential conflict of interest in relation to this article.

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James K. C. Wang, MD, is Assistant Professor of Obstetrics and Gynecology, Tufts University School of Medicine, and Medical Director of Wesson Women’s Clinic, Baystate Medical Center, Springfield, MA. James G. Gebhardt, MD, is Assistant Professor of Obstetrics and Gynecology, Tufts University School of Medicine, Baystate Medical Center, Springfield, MA.

References

1. Mathias SD, Kuppermann M, Liberman RF, Lipschutz RC, Steege JF. Chronic pelvic pain: prevalence, health-related quality of life, and economic correlates. Obstet Gynecol. 1996;87(3):321-327.
   
2. Reiter RC. A profile of women with chronic pelvic pain. Clin Obstet Gynecol. 1990;33(1):130-136.
3. Howard FM. The role of laparoscopy in chronic pelvic pain: promise and pitfalls. Obstet Gynecol Surv. 1993;48(6):357-387.
4. Howard FM. Chronic pelvic pain. Obstet Gynecol. 2003;101(3):594-611.
5. Montenegro ML, Gomide LB, Mateus-Vasconcelos EL, et al. Abdominal myofascial pain syndrome must be considered in the differential diagnosis of chronic pelvic pain. Eur J Obstet Gynecol Reprod Biol. 2009;147(1):21-24.
6. Howard FM, Perry P, Carter J, El-Minawi AM. Pelvic Pain: Diagnosis and Management. Philadelphia: Lippincott Williams and Wilkins; 2000:314-323.