Case of the Month #22: Post Mastectomy Pain by Dr Sonia Pierce

Persistent pain can occur following breast cancer-related operative procedures and, when following mastectomy, is referred to in the literature as Postmastectomy Pain Syndrome (PMPS) or Persistent Post-Mastectomy Pain (PPMP). The International Association for the Study of Pain (IASP) defines PMPS as persistent pain soon after mastectomy/lumpectomy affecting the anterior thorax, axilla, and/or medial upper arm¹. Pain can be severe enough to cause long-term disabilities, interfere with sleep and performance of daily activities, including use of the affected arm. The pain can also affect the patient's mood and social function and can add to costs for the health care system.

Mastectomy is one of the four surgical procedures at highest risk for transitioning from acute to persistent (chronic) pain², with up to 57% of patients experiencing pain 6 to 12 months after surgery³. The incidence of nerve injury or impairment and resultant chronic pain following a breast cancer operation ranges from 20 to 72 percent⁴. This variation can be partly explained by discrepancies in terms of definitions used to ascertain postmastectomy pain syndrome (PMPS), timing of assessment, or age group of the population studied. The prevalence also depends, in part, on the extensiveness of the breast and axillary procedure performed. A systematic review and meta-analysis of observational studies has suggested that almost half of all women undergoing breast cancer surgery develop persistent pain, and one in four develop moderate-to-severe PPSP⁴. The authors also conclude that a higher prevalence is associated with axillary lymph node dissection and chronic pain after breast cancer surgery persists for years without significant improvement in either prevalence or intensity⁴.

The differential diagnosis of PMPS includes recurrent breast cancer, metastatic

breast cancer, breast inflammation/infection –phantom breast pain or phantom sensations, lymphedema, musculoskeletal disorders, and cervical radiculopathy. A combination of clinical history taking, examination, appropriate imaging studies, electrodiagnostic studies, and the clinical presentation can help establish the diagnosis. PMPS may be caused by direct nerve injury (e.g., transection, compression, ischemia, stretching, retraction) during the breast cancer operation or the subsequent formation of a traumatic neuroma or scar tissue and possibly exacerbated by local radiation treatments and neurotoxic chemotherapies.

Patients with PMPS typically present with burning, electric shock, or stabbing pain and/or neuropathic symptoms (e.g., numbness, hyperesthesia, paraesthesia) at the operative site and/or the ipsilateral arm. Other symptoms of patients with PMPS include chest wall muscle pain, reduced range of motion of the shoulder, and reduced shoulder and/or hand grip strength. Findings on the physical examination include sensory changes at the operative site and/or ipsilateral extremity and decreased range of motion and strength in the ipsilateral arm.

Pre-operatively identifiable risk factors for PPMP include younger age, pre-existing pain, surgical and adjuvant treatment, and psychosocial factors, such as anxiety, depression, and catastrophising. Many strategies, including surgical technique modification and multimodal analgesia, have been applied to modify these factors in order to reduce incidence or alleviate the severity of PPMP². Regional anaesthesia techniques may alleviate the severity of acute postoperative pain, as well as theoretically prevent PPMP, as they decrease afferent nociceptive input and thus central sensitisation during the perioperative period².  

Inadequately controlled acute pain in the period after surgery is one of the risk factors for the development of chronic pain⁴.  Improving postoperative analgesia could greatly decrease the incidence of persistent postmastectomy pain; single-injection peripheral nerve blocks lasting less than 1 day have lowered persistent postmastectomy pain at 3 and 12 months^6,7. Improved pain relief in the immediate postoperative setting is not universally linked to lowered incidence of PPMP though, a recent double blind randomised trial demonstrated that paravertebral block did not reduce the incidence of chronic pain after breast surgery⁸.

There are a broad range of techniques used in PMPS management described in the literature, and we would like to signpost the reader to a comprehensive review of the treatments available for chronic pain after breast cancer-related surgery by Chappell et al⁹. This paper demonstrates diverse modalities that may provide pain relief, but the authors conclude by stating that no one solution is fail proof or without side effects. The authors support the role of multidisciplinary management for this patient population⁹. The paper by Tait et al¹⁰ also provides an overview of the physical, psychological and pharmacological therapies for PMPS. They comment that the identification of optimal pharmacotherapy is complicated by the multiplicity of potential contributing nociceptive factors, as well as the heterogeneity and variable quality of existing studies, conflicting data regarding benefits, side effect profiles, and drug interactions. They summarise that management requires a thorough patient assessment to identify the various factors associated with pain and dysfunction, therapy should target multiple contributing factors, when possible and pharmacotherapy may be a useful adjuvant to nonpharmacological strategies¹⁰.