Pain is a multidimensional experience and interacts with many aspects of an individual. In an attempt to standardize terminology, pain was defined by the International Association for the Study of Pain (IASP) in 19791 as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.” In their note about this definition, it is stated that “pain is always subjective” and individuals learn through experience what it means to be in pain. An individual can experience pain in the absence of actual tissue damage, thus avoiding “tying the pain to the stimulus.”1 The potential interplay and overlap of mental health and pain is present in the 1979 definition of pain, but the relationship has become more explicit in terms of the comorbidity of pain and other psychiatric diagnoses, the possible common pathophysiology, and the bidirectional influence which pain and psychiatric conditions have over each other.2 Updates to the 1979 definition have been suggested to incorporate the developmental, cognitive, and social aspects of how pain is perceived and treated3,4 in line with biopsychosocial models used in mental health. The US Institute of Medicine in 2011 published a report calling for taking a comprehensive view of chronic pain as a biological, biobehavioral, and societal condition and promoting changes in pain education, research, and treatment, which include a focus on prevention, pain as a public health problem, and a multidisciplinary approach to treatment that involves psychiatry.5
This chapter will discuss the pathophysiology of pain and its clinical presentation, with a focus on the overlap of pain and psychiatric conditions such as depression, anxiety, and others. Specific pain clinical entities of interest to neuropsychiatry to be reviewed include fibromyalgia (FM), complex regional pain syndrome (CRPS), and somatic symptom disorder (SSD) with predominant pain. We will then discuss the general approach to the assessment and treatment of pain conditions, with an emphasis on the comorbid presentation of pain and psychiatric disorders.
Chronic pain is defined as persistent or recurrent pain lasting longer than 3 months.6 Reports on the lifetime prevalence of chronic pain in developed countries vary, but it is estimated to affect about 20% of the adult population.7 In a study published in 2012, the estimated cost of chronic pain in the United States, including direct medical treatment costs and indirect costs due to lost productivity, was between 560 and 635 billion US dollars which exceeds the individual costs of heart disease, cancer, and diabetes.5,7
PATHOPHYSIOLOGY OF PAIN
Pain has always been an inherent part of medicine and is often the first sign of pathology that prompts a patient to present for medical care. The study of pain and the current body of evidence can describe how pain signals are transmitted to the brain. For example, how does ...