Before treating a patient, a psychologist must learn as many facts as possible about the patient and the situation. A history of physical symptoms and a psychosocial history help narrow down possible correlations and causes. Psychosocial history covers the family history of disorders and worries about illnesses, chronically ill parents, stress and negative life events, problems with family functioning, and school difficulties (academic and social).

These indicators may reveal whether there is a connection between stress-inducing events and an onset or increase in pain, and the removal in one leading to the removal in the other. They also may show if the patient gains something from being ill and how their reported pain matches medical records.

Physicians may refer a patient to a psychologist after conducting medical evaluations, learning about any psychosocial problems in the family, discussing possible connections of pain with stress, and assuring the patient that the treatment will be a combination between medical and psychological care. Psychologists must then do their best to find a way to measure the pain, perhaps by asking the patient to put it on a number scale. Pain questionnaires, screening instruments, interviews, and inventories may be conducted to discover the possibility of somatoform disorders. Projective tests may also be used.

At least once a week, 10-30% of those under 18 years of age suffer from unexplainable headaches and abdominal pains in the United States, and the number is rising. People from collectivistic countries such as Japan, China, and Mexico are more likely to suffer from pain disorder than individualistic countries such as the US and Sweden.

Psychogenic pain, also called psychalgia, is physical pain that is caused, increased, or prolonged by mental, emotional, or behavioral factors.

Headache, back pain, or stomach pain are some of the most common types of psychogenic pain. It may occur, rarely, in persons with a mental disorder, but more commonly it accompanies or is induced by social rejection, broken heart, grief, lovesickness, or other such emotional events.

Sufferers are often stigmatized, because both medical professionals and the general public tend to think that pain from psychological source is not "real". However, specialists consider that it is no less actual or hurtful than pain from other sources.

The International Association for the Study of Pain defines pain as "an unpleasant sensory and emotional experience associated with actual or potential tissue damage, "or described in terms of such damage"" (emphasis added). In the note accompanying that definition, the following can be found about pain that happens for psychological reasons:

Many people report pain in the absence of tissue damage or any likely pathophysiological cause; usually this happens for psychological reasons. There is usually no way to distinguish their experience from that due to tissue damage if we take the subjective report. If they regard their experience as pain and if they report it in the same ways as pain caused by tissue damage, it should be accepted as pain.

Medicine refers also to psychogenic pain or psychalgia as a form of chronic pain under the name of "persistent somatoform pain disorder" or "functional pain syndrome". Causes may be linked to stress, unexpressed emotional conflicts, psychosocial problems, or various mental disorders. Some specialists believe that psychogenic chronic pain exists as a protective distraction to keep dangerous repressed emotions such as anger or rage unconscious.

It remains controversial, however, that chronic pain might arise purely from emotional causes. Treatment may include psychotherapy, antidepressants, analgesics, and other remedies that are used for chronic pain in general.

Functional magnetic resonance imaging brain scanning has been used to measure pain, and correlates well with self-reported pain.

Below is a list of criteria for diagnosing TMS, according to Schechter and Sarno:

- "Lack of known physical cause:" Schechter and Sarno state that a physical examination, tests and imaging studies is needed to rule out serious conditions, such as tumors. Sarno considers spinal disc herniations to generally be harmless, because he says the symptom location does not even correlate to the herniation location.

- "Tender points:" While medical doctors use eleven of eighteen tender points as a diagnostic criteria for fibromyalgia, Sarno states that he uses six main tender points to diagnose TMS: two tender points in the upper trapezius muscles, two in the lumbar paraspinal muscles and two in the lateral upper buttocks. He states that these are found in 99% of TMS patients.

- "History of other psychosomatic disorders:" Schechter and Sarno consider a prior history of other psychosomatic disorders an indication that the patient may have TMS. They list irritable bowel syndrome and tension headache as examples of psychosomatic disorders.

Schechter and Sarno state that if a patient is unable to visit a medical doctor who is trained in TMS, then the patient should see a traditional medical doctor to rule out serious disorders, such as fractures, tumors and infections.

Historically, misdiagnosis rates have been high due to the complex nature of the disorder although some research now indicates that misdiagnosis may be reducing.

Inadequate treatment of pain is widespread throughout surgical wards, intensive care units, and accident and emergency departments In general practice, the management of all forms of chronic pain including cancer pain, and in end of life care. This neglect extends to all ages, from newborns to medically frail elderly. African and Hispanic Americans are more likely than others to suffer unnecessarily while in the care of a physician; and women's pain is more likely to be undertreated than men's.

The International Association for the Study of Pain advocates that the relief of pain should be recognized as a human right, that chronic pain should be considered a disease in its own right, and that pain medicine should have the full status of a medical specialty. It is a specialty only in China and Australia at this time. Elsewhere, pain medicine is a subspecialty under disciplines such as anesthesiology, physiatry, neurology, palliative medicine and psychiatry. In 2011, Human Rights Watch alerted that tens of millions of people worldwide are still denied access to inexpensive medications for severe pain.

Breastfeeding may decrease pain when babies are immunized.

A diagnosis of a functional neurological disorder is dependent on positive features from the history and examination.

Patients with functional movement disorders and limb weakness may experience symptom onset triggered by an episode of acute pain, a physical injury or physical trauma. They may also experience symptoms when faced with a psychological stressor, but this isn't the case for most patients. Patients with functional neurological disorders are more likely to have a history of another illness such as irritable bowel syndrome, chronic pelvic pain or fibromyalgia but this cannot be used to make a diagnosis.

FND does not show up on blood tests or structural brain imaging such as MRI or CT scanning. However, this is also the case for many other neurological conditions so negative investigations should not be used alone to make the diagnosis. FND can, however, occur alongside other neurological diseases and tests may show non-specific abnormalities which cause confusion for doctors and patients.

There is no single test that can fully diagnose fibromyalgia and there is debate over what should be considered essential diagnostic criteria and whether an objective diagnosis is possible. In most cases, people with fibromyalgia symptoms may also have laboratory test results that appear normal and many of their symptoms may mimic those of other rheumatic conditions such as arthritis or osteoporosis. The most widely accepted set of classification criteria for research purposes was elaborated in 1990 by the Multicenter Criteria Committee of the American College of Rheumatology. These criteria, which are known informally as "the ACR 1990", define fibromyalgia according to the presence of the following criteria:

- A history of widespread pain lasting more than three months – affecting all four quadrants of the body, i.e., both sides, and above and below the waist.

- Tender points – there are 18 designated possible tender points (although a person with the disorder may feel pain in other areas as well). Diagnosis is no longer based on the number of tender points.

The ACR criteria for the classification of patients were originally established as inclusion criteria for research purposes and were not intended for clinical diagnosis but have now become the "de facto" diagnostic criteria in the clinical setting. It should be noted that the number of tender points that may be active at any one time may vary with time and circumstance. A controversial study was done by a legal team looking to prove their client's disability based primarily on tender points and their widespread presence in non-litigious communities prompted the lead author of the ACR criteria to question now the useful validity of tender points in diagnosis. Use of control points has been used to cast doubt on whether a person has fibromyalgia, and to claim the person is malingering; however, no research has been done for the use of control points to diagnose fibromyalgia, and such diagnostic tests have been advised against, and people complaining of pain all over should still have fibromyalgia considered as a diagnosis.

In 2010, the American College of Rheumatology approved provisional revised diagnostic criteria for fibromyalgia that eliminated the 1990 criteria's reliance on tender point testing. The revised criteria use a widespread pain index (WPI) and symptom severity scale (SS) in place of tender point testing under the 1990 criteria. The WPI counts up to 19 general body areas in which the person has experienced pain in the preceding two weeks. The SS rates the severity of the person's fatigue, unrefreshed waking, cognitive symptoms, and general somatic symptoms, each on a scale from 0 to 3, for a composite score ranging from 0 to 12. The revised criteria for diagnosis are:

- WPI ≥ 7 and SS ≥ 5 "OR" WPI 3–6 and SS ≥ 9,

- Symptoms have been present at a similar level for at least three months, "and"

- No other diagnosable disorder otherwise explains the pain.

The DSM-IV-TR states that the fugue may have a duration from days to months, and recovery is usually rapid. However, some cases may be refractory. An individual usually has only one episode.

While psychogenic pain and pain disorder are accepted diagnoses in the medical community, the TMS modality is more controversial.

A non-peer-reviewed 2005 study by Schechter at the Seligman Medical Institute (SMI), co-authored with institute director Arthur Smith, found that treatment of TMS achieved a 57% success rate among patients with chronic back pain.

A peer-reviewed 2007 study with Schechter, Smith and Stanley Azen, Professor and Co-Director of Biostatistics in the Department of Preventative Medicine at the USC Keck School of Medicine, found a 54% success rate for treatment of TMS ("P"<.00001). The treatment consisted of office visits, at-home educational materials, writing about emotional issues and psychotherapy. The average pain duration for the study's patients was 9 years. Patients with less than 6 months of back pain were excluded to "control for the confounder that most back pain episodes typically resolve on their own in a few weeks."

Schechter, Smith and Azen also compared their results to the results of three studies of other psychological treatments for chronic back pain. The three non-TMS studies were selected because of (a) their quality, as judged by the Cochrane Collaboration, and (b) the similarity of their pain measurements to those used in the TMS study. Of the three non-TMS studies, only one (the Turner study) showed a statistically significant improvement. Compared to the 2007 TMS study, the Turner study had a lower success rate (26%-35%, depending on the type of psychological treatment) and a lower level of statistical significance ("P"<.05).

Schechter, "et al." state that one advantage of TMS treatment is that it avoids the risks associated with surgery and medication, but they caution that the risks of TMS treatment are somewhat unknown due to the relatively low number of patients studied so far.

The psychological mechanism of conversion can be the most difficult aspect of a conversion diagnosis. Even if there is a clear antecedent trauma or other possible psychological trigger, it is still not clear exactly how this gives rise to the symptoms observed. Patients with medically unexplained neurological symptoms may not have any psychological stressor, hence the use of the term "functional neurological symptom disorder" in DSM-V as opposed to "conversion disorder", and DSM-V's removal of the need for a psychological trigger.

In the opinion of Allen Frances, chair of the DSM-IV task force, the DSM-5's somatic symptom disorder brings with it a risk of mislabeling a sizable proportion of the population as mentally ill. “Millions of people could be mislabeled, with the burden falling disproportionately on women, because they are more likely to be casually dismissed as ‘catastrophizers’ when presenting with physical symptoms.”

The ICHD-2 lists diagnostic criteria for "persistent idiopathic facial pain" (the term that replaces AFP in this classification):

There are presently no accepted medical tests which consistently discriminate between facial pain syndromes or differentiate Atypical Facial Pain from other syndromes. However, a normal Radiograph, CT, and MRI may help to exclude other pathology such as arterio-veinous malformation, tumor, temporomandibular joint disorder, or MS.

Empirical studies have found that the prognosis for conversion disorder varies widely, with some cases resolving in weeks, and others enduring for years or decades. There is also evidence that there is no cure for Conversion Disorder, and that although patients may go into remission, they can relapse at any point. Furthermore, many patients who are 'cured' continue to have some degree of symptoms indefinitely.

AFP and AO can be difficult to diagnose, and are often misdiagnosed with resultant inappropriate attempts of treatment, e.g. root canal therapy which may at best have only a temporary benefit, or at worst lead to an increase in the pain. Excluding an organic cause for the pain is the most important part of the diagnosis. Odontogenic pain should especially be ruled out, since this accounts for over 95% of cases of orofacial pain.

There is considerable symptom overlap between atypical facial pain and temporomandibular joint dysfunction.

The diagnosis of facial pain generally is often multidisciplinary.

Somatic symptom disorder has been a controversial diagnosis, since it was historically based primarily on negative criteria - that is, the absence of a medical explanation for the presenting physical complaints. Consequently, any person suffering from a poorly understood illness can potentially fulfill the criteria for this psychiatric diagnosis, even if they exhibit no psychiatric symptoms in the conventional sense. In 2013-4, there were several widely publicized cases of individuals being involuntarily admitted to psychiatric wards on the basis of this diagnosis alone. This has raised concerns about the consequences of potential misuse of this diagnostic category.

Psychogenic disease (or psychogenic illness) is a name given to physical illnesses that are believed to arise from emotional or mental stressors, or from psychological or psychiatric disorders. It is most commonly applied to illnesses where a physical abnormality or other biomarker has not yet been identified. In the absence of such "biological" evidence of an underlying disease process, it is often assumed that the illness must have a psychological cause, even if the patient shows no indications of being under stress or of having a psychological or psychiatric disorder.

Examples of diseases that are believed by many to be psychogenic include psychogenic seizures, psychogenic polydipsia, psychogenic tremor and psychogenic pain.

There are problems with the assumption that all medically unexplained illness must have a psychological cause. It always remains possible that genetic, biochemical, electrophysiological or other abnormalities may be present which we do not have the technology or background to identify.

The term psychogenic disease is often used in a similar way to psychosomatic disease. However, the term "psychogenic" usually implies that psychological factors played a key causal role in the development of the illness. The term "psychosomatic" is often used in a broader way to describe illnesses with a known medical cause where psychological factors may nonetheless play a role (e.g., asthma can be exacerbated by anxiety).

A doctor may suspect dissociative fugue when people seem confused about their identity or are puzzled about their past or when confrontations challenge their new identity or absence of one. The doctor carefully reviews symptoms and does a physical examination to exclude physical disorders that may contribute to or cause memory loss. A psychological examination is also done.

Sometimes dissociative fugue cannot be diagnosed until people abruptly return to their pre-fugue identity and are distressed to find themselves in unfamiliar circumstances. The diagnosis is usually made retroactively when a doctor reviews the history and collects information that documents the circumstances before people left home, the travel itself, and the establishment of an alternative life.

Functional amnesia can also be situation specific, varying from all forms and variations of traumas or generally violent experiences, with the person experiencing severe memory loss for a particular trauma. Committing homicide; experiencing or committing a violent crime such as rape or torture; experiencing combat violence; attempting suicide; and being in automobile accidents and natural disasters have all induced cases of situation-specific amnesia (Arrigo & Pezdek, 1997; Kopelman, 2002a). As Kopelman (2002a) notes, however, care must be exercised in interpreting cases of psychogenic amnesia when there are compelling motives to feign memory deficits for legal or financial reasons. However, although some fraction of psychogenic amnesia cases can be explained in this fashion, it is generally acknowledged that true cases are not uncommon. Both global and situationally specific amnesia are often distinguished from the organic amnesic syndrome, in that the capacity to store new memories and experiences remains intact. Given the very delicate and often times dramatic nature of memory loss in these such cases, there usually is a concerted effort to help the person recover their identity and history. This will allow the subject to sometimes be recovered spontaneously when particular cures are encountered.

The utility of PTSD derived psychotherapies for assisting children with C-PTSD is uncertain. This area of diagnosis and treatment calls for caution in use of the category C-PTSD. Ford and van der Kolk have suggested that C-PTSD may not be as useful a category for diagnosis and treatment of children as a proposed category of developmental trauma disorder (DTD). For DTD to be diagnosed it requires a

'history of exposure to early life developmentally adverse interpersonal trauma such as sexual abuse, physical abuse, violence, traumatic losses of other significant disruption or betrayal of the child's relationships with primary caregivers, which has been postulated as an etiological basis for complex traumatic stress disorders. Diagnosis, treatment planning and outcome are always relational.'

Since C-PTSD or DTD in children is often caused by chronic maltreatment, neglect or abuse in a care-giving relationship the first element of the biopsychosocial system to address is that relationship. This invariably involves some sort of child protection agency. This both widens the range of support that can be given to the child but also the complexity of the situation, since the agency's statutory legal obligations may then need to be enforced.

A number of practical, therapeutic and ethical principles for assessment and intervention have been developed and explored in the field:

- Identifying and addressing threats to the child's or family's safety and stability are the first priority.

- A relational bridge must be developed to engage, retain and maximize the benefit for the child and caregiver.

- Diagnosis, treatment planning and outcome monitoring are always relational (and) strengths based.

- All phases of treatment should aim to enhance self-regulation competencies.

- Determining with whom, when and how to address traumatic memories.

- Preventing and managing relational discontinuities and psychosocial crises.

Functional assessment of brain activity can be assessed for psychogenic amnesia using imaging techniques such as fMRI, PET and EEG, in accordance with clinical data. Some research has suggested that organic and psychogenic amnesia to some extent share the involvement of the same structures of the temporo-frontal region in the brain. It has been suggested that deficits in episodic memory may be attributable to dysfunction in the limbic system, while self-identity deficits have been suggested as attributable to functional changes related to the posterior parietal cortex. To reiterate however, care must be taken when attempting to define causation as only "ad hoc" reasoning about the aetiology of psychogenic amnesia is possible, which means cause and consequence can be infeasible to untangle.

BMS is a diagnosis of exclusion, i.e. all other explanations for the symptoms are ruled out before the diagnosis is made. There are no clinically useful investigations that would help to support a diagnosis of BMS (by definition all tests would have normal results), but blood tests and / or urinalysis may be useful to rule out anemia, deficiency states, hypothyroidism and diabetes. Investigation of a dry mouth symptom may involve sialometry, which objectively determines if there is any reduction of the salivary flow rate (hyposalivation). Oral candidiasis can be tested for with use of a swabs, smears, an oral rinse or saliva samples. It has been suggested that allergy testing ("e.g.", patch test) is inappropriate in the absence of a clear history and clinical signs in people with a burning sensation in the mouth. The diagnosis of a people with a burning symptom may also involve psychologic screening e.g. depression questionnaires.

The second edition of the International Classification of Headache Disorders lists diagnostic criteria for "Glossodynia and Sore Mouth":

One form of treatment is Cognitive behavioral therapy which promotes desensitization methods.

SPS is diagnosed by evaluating clinical findings and excluding other conditions. There is no specific laboratory test that confirms its presence. Underdiagnosis and misdiagnosis are common.

The presence of antibodies against GAD is the best indication of the condition that can be detected by blood and cerebrospinal fluid (CSF) testing. Anti-GAD65 is found in about 80 percent of SPS patients. Anti-thyroid, anti-intrinsic factor, anti-nuclear, anti-RNP, and anti-gliadin are also often present in blood tests. Electromyography (EMG) demonstrates involuntary motor unit firing in SPS patients. EMG can confirm the diagnosis by noting spasms in distant muscles as a result of subnoxious stimulation of cutaneous or mixed nerves. Responsiveness to diazepam helps confirm that the patient is suffering from SPS, as this decreases stiffness and motor unit potential firing.

The same general criteria are used to diagnose paraneoplastic SPS as the normal form of the condition. Once SPS is diagnosed, poor response to conventional therapies and the presence of cancer indicate that it may be paraneoplastic. CT scans are indicated for SPS patients who respond poorly to therapy to determine if this is the case.

A variety of conditions have similar symptoms to SPS, including myelopathies, dystonias, spinocerebellar degenerations, primary lateral sclerosis, neuromyotonia, and some psychogenic disorders. Tetanus, neuroleptic malignant syndrome, malignant hyperpyrexia, chronic spinal interneuronitis, serotonin syndrome, Multiple sclerosis, Parkinson's disease, and Isaacs syndrome should also be excluded.

Patients' fears and phobias often incorrectly lead doctors to think their symptoms are psychogenic, and they are sometimes suspected of malingering. It takes an average of six years after the onset of symptoms before the disease is diagnosed.