ASRA Pain Medicine Update

Epidemiology

Breast cancer is the most common cancer among women in the United States. An estimated one of eight women will develop breast cancer in her lifetime, resulting in approximately 300,000 new cases per year.^[1]

Postmastectomy pain syndrome (PMPS) itself is not a specific diagnosis but rather describes a cluster of symptoms frequently observed in breast cancer survivors following treatment. Its name is a misnomer, because symptoms and impairments can be seen following mastectomy, lumpectomy, lymph node dissection, and reconstruction, as well as chemotherapy and radiation. Generally, it is considered to be chronic breast or chest wall pain lasting at least 3 months following cancer treatment.^[2] Although an exact definition or specific criteria have not been established, incidence rates are estimated at 40–50%.^[1],[3] Cancer rehabilitation physicians, as subspecialists of physical medicine and rehabilitation, diagnose and treat PMPS as part of comprehensive breast cancer rehabilitation programs.

Clinical Presentation and Differential Diagnosis

Many patients will experience short-term nociceptive pain after breast cancer treatment. However, with PMPS, patients frequently experience persistent neuropathic-type pain: burning, tingling, aching, a subjective sense of “tightness” around the chest wall, or even phantom breast or nipple pain. Neuropathic pain results from dysfunction of the peripheral nerves caused by surgery, radiation, or neurotoxic chemotherapies.^[4]

Many patients will experience short-term nociceptive pain after breast cancer treatment. However, with PMPS, patients frequently experience persistent neuropathic-type pain.

Neuromas, frequently found in scars following breast or axillary incisions, are one cause of neuropathic pain and can become chronic. Although they can occur after simple lumpectomies, they are more common following more extensive surgeries such as axillary lymph node dissections (ALNDs) and with the addition of radiation.^[5] Damaged nerves are easily excitatory, sending a constant barrage of painful impulses with the slightest mechanical distortion.^[6] Commonly transected nerves include intercostal, thoracodorsal, medial and lateral pectoral, and long thoracic nerves.^[7]

A well-recognized cause of PMPS is intercostobrachial neuralgia. The intercostobrachial nerve is the lateral cutaneous branch of the second intercostal nerve, arising from T2. It provides sensation to the medial upper arm, axilla, and lateral chest wall. It is frequently sacrificed during ALND and almost always results in numbness. However, in symptomatic patients, it can result in painful paresthesias and chronic neuropathic pain.^[8]

Musculoskeletal pain syndromes are a common cause of nociceptive-type pain and, when chronic, should be included in the definition of PMPS. Chest wall pain that is persistent beyond simple incisional pain can be the result of scarring of the incised tissues, leading to hypomobile tissue adhered to the underlying chest wall. Another example of postmastectomy musculoskeletal pain is rotator cuff dysfunction. One cause of this is the result of changes in scapulothoracic motion.^[9] Pectoralis major muscle tightness or spasms, resulting from tissue expanders or radiation, pull the acromion into a protracted and inferior position and lessen the subacromial space through which the rotator cuff tendons pass, causing rotator cuff tendinopathies.^[10]

Etiology

The etiology of PMPS is multifactorial. The severity of postoperative pain has been shown to increase the risk of developing chronic pain in various surgeries with the hypothesis of central desensitization.^[11] In a study by Tasmuth et al,^[12] patients with chronic breast pain used significantly more analgesics in the 48 hours following surgery than those without chronic pain. This is especially important given that postoperative pain is a modifiable risk factor, using preoperative analgesia and nerve blocks.

Researchers have hypothesized that younger patients are more predisposed to developing chronic pain, including PMPS.^[13] Younger patients may be more sensitive to nerve damage, have higher preoperative anxiety, and receive more aggressive treatment.^[14] Surgical factors contributing to PMPS include a more extensive axillary lymph node dissection because it leads to greater injury of the intercostobrachial nerve, resulting in neuropathic pain.^[15],[16] Postoperative radiation therapy to the axilla increases nerve damage and can lead to persistent pain that can last months to years following treatment, even in patients who undergo breast conservation surgery.^[12] Psychosocial factors such as depression, anxiety, and catastrophizing have been shown to increase postoperative pain and chronic pain following breast surgery,^[17] but this is another modifiable risk factor.^[18]

Treatment of PMPS includes rehabilitation interventions, medications, and interventional procedures. Stretching and active exercises are used to treat impaired range of motion of the shoulder and strengthen scapular stabilizers, and myofascial techniques are helpful for incisional pain and axillary cording.^[4],[19] Pharmacologic interventions are aimed at reducing neuropathic pain (see Table 1 for commonly prescribed medications). Interventional techniques include intercostobrachial nerve blocks and the superficial and deep serratus blocks.^[20],[21] Hydrodissection of the pectoralis muscles can alleviate pain after reconstruction.

Risk reduction strategies include maximizing perioperative pain management with gabapentin, venlafaxine, and topical lidocaine.^[22],[23] Paravertebral and pectoral nerve blocks have been used to limit postoperative pain, with the potential of reducing the development of chronic pain.^[24] Providing perioperative psychosocial support may enhance postoperative recovery and decrease the incidence of chronic breast pain.

Summary

PMPS is a constellation of symptoms leading to chronic breast and chest wall pain in patients with breast cancer and impairing quality of life. Future research is needed to improve recognition, risk factor modification, and treatment.

References

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19. De Groef A, Van Kampen M, Dieltjens E, et al. Effectiveness of postoperative physical therapy for upper-limb impairments after breast cancer treatment: a systematic review. Arch Phys Med Rehabil 2015;96:1140–1153.
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