Sorting the array of symptoms encountered in an office visit is an ongoing challenge. Unlike physical signs, symptoms are not observable. Traditionally, dualistic or binary explanatory models of symptoms have prevailed. Symptoms have been viewed as psychological, reflecting a mental or emotional state, or physical, relating to a body sensation such as pain, fatigue, or palpitations. Physical symptoms, often termed somatic in the mental health literature, prompt more than 50% of U.S. office visits.10 Common somatic complaints include: pain from headache, backache, or musculoskeletal conditions; gastrointestinal symptoms; sexual or reproductive symptoms; and neurologic symptoms such as dizziness or loss of balance.

Approximately 5% of somatic symptoms are acute, triggering immediate evaluation.11 Another 70% to 75% are minor or self-limited and resolve in 6 weeks. Nevertheless, approximately 25% of patients have persisting and recurrent symptoms that elude assessment and fail to improve. Overall, 30% of symptoms are medically unexplained. Some involve single complaints that persist longer than others, for example, back pain, headache, or musculoskeletal pain. Others present as clusters in functional syndromes, such as irritable bowel syndrome, fibromyalgia, chronic fatigue, temporomandibular joint disorder, and multiple chemical sensitivity.

Experts now propose that physical and psychological symptoms are interactive and represent "a varying mix of disease and nondisease input" that lies along a spectrum from medical to mental disorders. Evidence shows that symptom etiology is often multifactorial, lacking a single cause; and that often, there are several related symptoms or symptom clusters rather than single complaints.The integrative continuum model leads to explanations that are less likely to be "simplified, reductionistic, or mechanistic." Watch for emerging schemas that place symptoms along a causative spectrum with five nodal points: symptoms like wheezing, with a clear medical cause; functional somatic syndromes like irritable bowel syndrome; "symptom-only diagnoses" such as low back pain; symptoms associated with psychological conditions, like fatigue in depression; and finally, medically unexplained symptoms.

Changes have also occurred in the classification of somatic syndromes in the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) of 2013. When patients have "distressing somatic symptoms plus abnormal thoughts, feelings, and behaviors in response to these symptoms," clinicians can consider the diagnosis of somatic symptom and related disorders. These patients have prominent somatic symptoms associated with significant distress and impairment and are seen more often in primary care and medical settings than in psychiatric and mental health settings. They may have accompanying medical disorders. The DSM-5 notes that "a distinctive characteristic of the many individuals with somatic symptom disorder is not the somatic symptoms per se, but instead the way they present and interpret them." This change in diagnostic criteria emphasizes the presence of positive symptoms, and moves away from relying on medically unexplained symptoms and the absence of a medical cause, which can be difficult to determine. The prevalence of somatic symptom disorders is estimated at 5% to 7%.

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