It is rare for abdominal, pelvic or hip disease to mimic spondylotic or idiopathic low back pain, but a few specific diseases are important. The most common is likely to be metastatic disease to the lumbar spine which can be diagnosed with appropriate imaging. Retroperitoneal inflammatory disease or cancer are other definable causes. Chronic pelvic inflammatory disease and endometriosis both produce low back pain and leg pain. Aortic aneurysm may produce chronic back pain associated with vascular claudication, although dissection is usually an acutely painful event. Intra-abdominal disease of other organs is so rarely confused with idiopathic chronic back pain that any are unlikely to be important in diagnosis. Renal, gallbladder and bowel disease are so commonly associated with other symptoms that confusion in diagnosis is unlikely to occur.There is a strong tendency among physicians and many others involved in the treatment of chronic pain to assume that all pain for which no diagnosable cause can be found is psychosomatic. Nowhere where is this more true than with chronic back pain. The National Low Back Pain Study data indicates that the incidence of psychopathology is no greater in back pain patients than would be expected in any ill population. Three per cent of patients in that study had a psychiatric diagnosis which was thought by the examiners to be the primary cause of the complaint. However, in a population of more than 2000 patients admitted to a pain treatment programme for manifestations of the chronic pain syndrome, the incidence of psychopathology was much higher. Between 15 and 20% of these patients had a primary psychiatric diagnosis which was thought to be the origin of the pain complaint or at least an important mediator. Endogenous depression was the most common diag-nosis. The psychiatrists involved with these patients separated this diagnosis from the reactive depression seen much more commonly. Somatiform disorder was the next most common diagnosis made, followed by schizophrenia. There is an important difference of opinion among pain specialists about what is the most common diagnosis in some experiences, personality disorder. Some experts find an increased incidence of diagnosable personality disorder among patients with chronic pain syndrome. Others note the increased frequency of symptoms suggestive of personality disorder without a truly diagnosable syndrome by DSM criteria. Often, there is imprecise separation of psychosocial symptoms which follow an acute pain event and those which are present antecedent to the noxious event. Then, there is the added factor that the presence of a psychiatric diagnosis or these personality traits does not eliminate the possibility of a bona fide painful problem with the back. This chapter is not the place for an exhaustive review of these psychological factors. In this context, it is only important to emphasize that psychiatric disease may have pain as an important symptom. The presence of psychiatric disease does not eliminate the probability that the patient has a diagnosable separate cause. The presence of traits suggestive of personality disorder cannot be construed as causative of the complaint of back pain. However, the increased incidence of co-morbidities which will be discussed under the heading of chronic pain syndrome in patients with these traits is important therapy ( Waddell et al 1980 ).
It is much more likely that symptoms in patients with idiopathic low back pain are ascribed to psychosomatic causes than for patients with symptoms secondary to psychiatric disease to be misdiagnosed as organic problems. In typical patients with chronic back pain, psychological issues are uncommon. Even in the so-called chronic pain syndrome, overt psychiatric disease is unusual. The psychosomatic side of disability compensation is poorly defined at present, but may be more important than in the general population. The chicken–egg issue of psychiatric symptoms in chronic pain syndrome is not yet settled and deserves further investigation.