Spectrums of conditions

Psychiatric diagnostic constructs often have no zones of rarity between different diagnostic constructs, and they often co-occur. This happens even where clear disease processes are involved, such as the dementias. They may represent different areas of a spectrum of illness/condition and/or be part of a spectrum of illnesses/conditions. However, they share both these characteristics with many general medical diagnostic constructs. For spectrums of illness/condition this may be because there are no natural boundaries but that it is important or seems obvious to recognize different areas of the spectrum for reasons of clinical utility (such as different prognostic implications or treatments) or different clinical pictures. For spectrums of illnesses/conditions the reason for co-occurrence may be because different diagnostic constructs have similar causes/mechanisms. On the other hand, these problems of lack of boundaries are not present as commonly in general medical diagnostic constructs. Alternative mental health classifications do not have the same issues with co-occurrence. They may be more useful in research to discover reasons why co-occurrence of symptoms may occur but have pragmatic drawbacks for other classification functions.

Reliability of diagnosis

Reliability of a diagnosis can be measured as either agreement with a reference criterion or agreement between clinicians as to a diagnosis. Most psychiatric and some general medical diagnostic constructs are identified on the basis of a clinical picture, not using a reference criterion such as laboratory tests. Most psychiatric diagnostic constructs have moderate to substantial reliability in research studies. They are likely to be less reliable in clinical practice. Measures such as standardizing interviews can improve reliability. General medical diagnostic constructs have similar reliability to psychiatric diagnostic constructs in research studies and are also likely to be less reliable in clinical practice. Even with laboratory tests, some medical conditions are hard to distinguish due to similarities in their clinical pictures. For alternative mental health classifications, psychological formulation—except psychodynamic formulation—is less reliable than psychiatric diagnosis. Symptom-based classification has at least equal reliability to psychiatric diagnosis. Dimension-based classification has equivalent reliability to psychiatric diagnosis. These may be combined with diagnosis but may have less usefulness on their own for other functions, e.g. administrative.

Multidisciplinary working, evidence, treatment, and decision-making in medicine

Patients have many needs and not all can be met using the medical model, hence the necessity of multiple therapeutic models and multidisciplinary working. Doctors’ sapiental role relies on evidence from research which can vary in quality. Quantitative and qualitative research are both useful. Randomized controlled trials with blinded assessments are the best method of assessing treatment effectiveness. Objectives of treatment should be jointly decided between doctor and patient and are often not simply about cure. Mechanisms of action of intervention do not always reverse disease progress but may involve other processes such as indirect compensation. Medication has many complex effects, both therapeutic and adverse. The medical model allows doctors to see many patients and work in emergency situations including providing overnight cover. This is because after the initial assessment, further assessments can be brief and if medication is used it is usually taken outside consultations. This ability to see many patients at all hours means mental health services will often include doctors using the medical model.

The nature of diagnostic constructs

Classification is essential in medicine to help doctors acquire, learn, and recall clinically useful information about problems coming to healthcare professionals’ attention. There problems include both essentialist diagnostic constructs (where all examples share a quality and are distinct from other constructs) and nominalist diagnostic constructs (used to describe clinically useful concepts not necessarily separate from other constructs). Diagnostic constructs may be recognized using defined criteria and/or as prototypical examples. They are based on similarities in clinical picture, mechanisms/processes, and/or causes. They may be used to identify clinically important situations, diseases/clear-cut syndromes, spectrums of health, illness(es)/and condition(s), injuries, and other situations of interest to healthcare professionals. Thresholds established on the basis of clinical utility (e.g. level of distress or risk of complications) may be used to define conditions. Care must be taken to guard against over-medicalization of problems or situations.

The role of diagnosis in medical practice and society

Organization of knowledge is needed to help doctors learn and recall information in their clinical practice. Diagnostic constructs help, providing prototypes against which doctors can diagnose patient conditions. They then seek to confirm or disprove this diagnosis by searching for relevant information. Attached to these diagnostic constructs are information such as causes, prognosis, and treatment. Diagnostic constructs are provisional and should be changed if information suggests they are incorrect. They also aid communication between professionals for teaching and research, and have important social functions such as providing access to healthcare, determining eligibility for welfare, offering administrative and payment functions, and collecting health statistics. Some social effects of diagnostic constructs can be harmful, such as stigma. Diagnostic constructs are included in broad diagnostic formulations including relevant clinical information.

Variability of clinical picture

Psychiatric diagnostic constructs produce highly variable clinical pictures in patients. Amongst the reasons for this are high rates of co-occurrence of different diagnostic constructs, which themselves are often polythetic in nature. People who meet criteria for a diagnostic construct may have little or even no clinical features in common. These diagnostic constructs rely on people meeting the diagnostic criteria having similar qualities to their condition such as similar likelihoods of outcomes/responses to treatments. These highly variable clinical pictures are seen even when clear disease is involved, such as the dementias. General medical diagnostic constructs can also display highly variable clinical pictures even when clear disease processes have been identified. Polythetic diagnostic criteria decided upon by expert committees are also used for general medical diagnostic constructs which can also result in people meeting the same diagnostic criteria having little in common in their clinical pictures. Co-occurrence is also common in general medicine. Psychological formulation does not have to address the issue of variable clinical pictures. Both symptom-based and dimensional classifications can depict variable clinical pictures more accurately than diagnostic constructs but there are pragmatic issues such as suitability for brief appointments or emergency work.

Spectrums of health

Many conditions in psychiatry cannot be separated from normality/healthy states (e.g. depression) but even these broad diagnostic constructs may include syndromes like melancholia. There is still a debate as to whether psychotic-like experiences in the community are on a continuum with psychotic symptoms in those meeting diagnostic criteria for psychosis diagnostic constructs. Schizophrenia may exist on a continuum with related conditions (e.g. schizotypal personality disorder). There are differences between people meeting criteria for schizophrenia and healthy controls but none that can be used as a diagnostic test to separate the two, with the possible exception of anomalous self-experiences differentiating schizophrenia spectrum conditions from healthy controls and other diagnostic constructs. Several general medical conditions also exist on a continuum with health with no zones of rarity (e.g. hypertension and type 2 diabetes). Thresholds to meet criteria for these diagnostic constructs are chosen by expert committees often based on risk of developing complications (e.g. myocardial infarctions) and/or whether medical intervention may be beneficial. Even reasonably objective investigations can give abnormal results in healthy people. Concerns about whether thresholds are too low, leading to over-diagnosis, unnecessary treatment, and iatrogenic harm, also exist in general medicine. Other classifications in mental health will need to use thresholds in order to fulfil functions such as administration, research, or access to services. Dimensional classifications are good at representing the many spectrums of mental health.

Criticism of psychiatric treatment

Criticisms of psychiatric treatment often involve comparison to idealized depictions of general medical treatment. Psychiatric treatments are described as not reversing diseases but many treatments in general medicine also do not reverse disease and some have unknown mechanisms. It is stated that psychiatrists prescribe medication to reverse hypothesized mechanisms, but a survey found they usually prescribed a medication in a clinical situation because research had shown it to be effective, even though the mechanism of action was unclear. Antidepressants are said to be ineffective because of a small overall effect averaged over groups of participants but this ignores evidence that some people will derive a significant clinical benefit. Antipsychotics are effective in preventing relapse of psychosis in research studies; for a variety of reasons, withdrawal-induced psychosis is unlikely to explain enough of this advantage to prove the claim that antipsychotics are ineffective. Although lithium research trials are imperfect, including reporting high rates of lithium withdrawal-induced mania, there is still some evidence of benefit in acute mania and of modest benefit in preventing relapse of bipolar disorder in those who can continue lithium for two years or more. Questions comparing psychiatric and general medical treatments were generated.

Treatments in psychiatry compared to general medicine

There is clear overlap in effectiveness between psychiatric treatments and general medicine medications. Both psychiatric treatments and general medicine medications can be harmful. Mechanisms of action of psychiatric treatments are often obscure or unknown. This is less common in general medicine medication but some of the most commonly prescribed drugs used in general medicine do not cure or act directly on disease mechanisms. Evidence-based psychotherapy is an effective treatment for many mental health conditions; its relative effectiveness compared to psychiatric medication varies depending on the condition. If the client is willing and able to participate in bona fide psychotherapy with evidence of effectiveness, it may be preferable to psychiatric medication as it seems to have less serious adverse effects although more research is needed on harmful adverse effects. Psychotherapy combined with medication is often more effective than either used alone and both types of treatment are complementary, even synergistic, in achieving treatment objectives. Access to psychotherapy is often less easy than access to medication as it is labour intensive, and using medication allows doctors to see many more patients (see Chapter 5). For some conditions and situations, for example, for those unable to participate in psychotherapy, psychiatric treatments are still preferred.

Biological factors and health

There is often a lack of identified causal biological mechanisms or biological differences of structure or process for many psychiatric diagnostic constructs. There is a lack of useful biomarkers common to all people who meet criteria for a psychiatric diagnostic construct that differentiates them from the healthy population. This can also be the case for general medical conditions for both aetiology and differences in structure or process and sometimes lack of useful biomarkers but this occurs to a lesser extent. There are also occasions when medical conditions cause mental health problems directly. For this reason doctors will always be involved in mental health to some degree and will use diagnostic constructs to describe these conditions as they are familiar with diagnosis in their medical practice. There are examples of clear biological abnormalities that are often detected accidentally that do not require treatment. Medically unexplained or functional symptoms/syndromes are commonly seen in general medicine, although the term ‘medically unexplained’ is contentious. Many diagnostic constructs—medical or psychiatric—involve complex polygenetic interactions with the environment.