The relationship between depression and dementia is complex. Depression appears to be an independent risk factor for incident dementia, conferring a two-fold increase in dementia risk. Depression may represent an early sign or prodromal feature of dementia. The association between depression and dementia appears to strengthen as the interval between the two disorders shortens. Depression may also be a consequence of dementia.

Vascular dementia describes chronic progressive impairment of cognitive function arising from cerebrovascular injury. The presentation of vascular dementia is often insidious, with disorganisation, loss of drive, irritability, mental rigidity, difficulties with planning and problem solving, emotional lability and other mood changes, and sometimes inappropriate or disinhibited social behaviour. Physical examination may identify gait impairment, bradykinesia, rigidity, and focal neurological signs. 

Mild cognitive impairment (MCI) is a heterogeneous clinical syndrome defined as evidence of cognitive decline which is greater than expected for an individual’s age and educational level but which does not significantly impact on activities of daily living. The challenge for clinicians is to distinguish between normal cognition, cognitive decline normal for ageing, subjective cognitive decline, delirium, MCI and dementia. The history should focus on the onset and progression of symptoms. An acute or fluctuating course suggests delirium or another potentially reversible cause.

Substance use disorder (SUD) encompasses the use of drugs (illicit and prescription) or alcohol in a way that may cause harm and is difficult to control. Diagnosis is based on clinical history and examination in accordance with ICD-11 criteria which categorise use as hazardous, harmful or dependent. People often see their GP for a medical problem arising from SUD without mentioning substance use. Good rapport and an empathetic attitude can facilitate disclosure. 

Bipolar disorder is a complex, recurrent, severe and potentially lifelong mental illness. The peak age of onset is 15-19 years, with most cases developing before the age of 30. It is crucial to distinguish bipolar from unipolar depression not only as an essential starting point for appropriate treatment and risk management, but also to avoid antidepressant monotherapy which can exacerbate the frequency and severity of mood symptoms and cause resistance to appropriate medications.

Obsessive compulsive disorder (OCD) consists of obsessions (repetitive, intrusive thoughts, urges, impulses or doubts) and compulsions (ritualistic, deliberate behaviours performed in response to obsessions). As well as contamination and safety fears, many patients experience distressing thoughts of causing harm. Sexual obsessions are common, including thoughts regarding sexual orientation, aggressive sexual behaviour or child molestation. Typical compulsions include checking, washing, ruminating, and counting.

Psychosis is a state of mind in which a person loses contact with reality in at least one important respect while not intoxicated with, or withdrawing from, alcohol or drugs, and while not affected by an acute physical illness that better accounts for the symptoms. Common positive symptoms of psychosis include delusions and hallucinations. These symptoms are strongly influenced by the underlying cause of the psychosis: delusions in schizophrenia tend to be bizarre; delusions in depression negative; delusions in mania expansive. When a patient presents with psychotic symptoms, it is important to take a full psychiatric history, perform a mental state examination and complete relevant investigations, as indicated in each individual case.

Schizophrenia often runs a chronic course and is associated with considerable morbidity and mortality. While psychotic symptoms are the most obvious manifestations of the condition, negative symptoms (e.g. apathy and withdrawal) and cognitive symptoms (especially deficits in executive function) are often more disabling. It generally presents in late adolescence or early adulthood. Schizophrenia typically develops insidiously, potentially over several years. The GP is ideally placed to respond to family concerns, identify prodromal symptoms, screen for psychotic symptoms and initiate either a mental health review or active monitoring in primary care.

Co-occurring severe mental illness, usually schizophrenia or bipolar affective disorder, and substance misuse is termed dual diagnosis. Mental illness and its consequences may lead to substance misuse as a coping strategy. Substance misuse can lead to mental health problems, either by triggering a first episode in a susceptible person, or by exacerbating an existing disorder. However, substance misuse itself is unlikely to be the sole cause of a severe and enduring mental illness.

Autism covers a wide spectrum across the dimensions of social communication, repetitive and stereotyped behaviours as well as other non-clinical and cognitive features. Individuals with autism can function well in certain environments, where there are fewer demands to multitask and factual information and pattern recognition are required, but they may not function well in highly social environments, or situations characterised by rapid and unpredictable change.

It is estimated that up to 80% of patients with Parkinson’s disease will eventually develop cognitive impairment over the course of their illness. Even at the time of diagnosis, cognitive impairment has been reported in 20-25% of patients. Commonly affected domains are executive function, visuospatial ability and attention control. In addition, patients with Parkinson’s disease dementia may present with deficits in language function and verbal memory.

The prevalence of mild cognitive impairment in adults aged 65 and over is estimated to be 10-20%. It is likely that this figure will increase in line with trends in dementia diagnosis. In some cases, mild cognitive impairment may be a prodrome for dementia, and may be caused by any of the dementia pathology subtypes. It is important to obtain a history of cognitive changes over time, as well as information about the onset and nature of cognitive symptoms, confirmed by a reliable informant, if available.

The diagnosis of post-traumatic stress disorder (PTSD) differs from most psychiatric disorders as it includes an aetiological factor, the traumatic event, as a core criterion. The DSM 5 core symptoms of PTSD are grouped into four key symptom clusters: re-experiencing, avoidance, negative cognitions and mood, and arousal. Symptoms must be present for at least one month and cause functional impairment.

The most common causes of young onset dementia are early onset forms of adult neurodegenerative conditions and alcohol. Vascular dementia is the second most common cause of young onset dementia after Alzheimer’s disease. Conventional vascular risk factors may be absent and diagnosis relies on imaging evidence of cerebrovascular disease. Those with suspected young onset dementia should be referred to a neurology-led cognitive disorders clinic where available as the differential diagnosis is considerably broader than in older adults and requires specialist investigation.

Major (unipolar) depression is one of the most common mental health disorders in children and adolescents, with an estimated one year prevalence of 4-5% in mid-late adolescence. Depression is probably the single most important risk factor for teenage suicide, the second to third leading cause of death in this age group and a forerunner of adult depressive disorder. Half of those with lifelong recurrent depression started to develop their symptoms before the age of 15 years.

NICE recommends that when adults present in primary care with depression, they should be asked about previous periods of overactivity or disinhibited behaviour. If this behaviour lasted for four or more days referral for a specialist mental health assessment should be considered. A diagnosis of bipolar disorder is supported by diagnostic criteria and usually confirmed by a psychiatrist. If a manic episode has been present during the history the diagnosis is bipolar I disorder, while a hypomanic episode is indicative of bipolar II disorder.

Depression is more common in old age than dementia yet is underdiagnosed and undertreated. It is important to recognise that patients may not always present in a typical way, features that may indicate depression include anxiety, a preoccupation with somatic symptoms, and a change in function. The presence of understandable triggers and causes should not deter GPs from offering treatment, as long as symptoms are pervasive and continuously persist beyond two weeks.

Schizophrenia is a debilitating, often chronic, psychotic disorder with early onset and a lifetime prevalence of 7.2/1,000. The longer the period without treatment, the worse the outcome. In the UK, the mean duration of untreated psychosis is one to two years. The new NICE guidelines for schizophrenia recommend that all patients who are distressed and have a decline in social functioning accompanied by psychotic symptoms or behaviour suggesting psychosis should be comprehensively assessed by a specialist mental health service.

Autism affects 1.1% of the adult population. High-functioning individuals with autism, Asperger’s syndrome, may remain undiagnosed until adulthood. Autism is a life-long condition characterised by problems in two core dimensions: difficulties with social communication and strongly repetitive behaviour, resistance to change or restricted interests. The history should identify early developmental and behavioural problems in different settings e.g. at home, in education or employment. Sensory and GI problems are very common, and should be asked about. The Autism-Spectrum Quotient (AQ-10) is a 10-item questionnaire for people with suspected autism. It provides a time-efficient, structured way of ascertaining key symptoms and clearly signals those who should be referred for further assessment.

The age at which individuals are most physically aggressive is 22 months. However, some children fail to inhibit this normal aggression and by the time they are three or four are showing signs of oppositional defiant disorder. In older children persistent antisocial behaviour is classified as conduct disorder. Epidemiological follow-up surveys show that the risk of poor outcomes in antisocial children is very high. The causes are multiple but two sets of factors stand out. First, genetic predisposition. Even children adopted away from violent or criminal parents have three or four times the rate of antisocial behaviour and second, poor parenting. [With external links to the evidence base]

In perinatal mental illness not only does the patient suffer, but obstetric outcomes, mother-baby interactions and hence longer term emotional and cognitive development of the child are also affected. Perinatal mental illness also has an impact on other family members. The UK Confidential Enquiry into Maternal and Child Health has consistently found psychiatric disorders to be one of the leading causes of maternal death, often through suicide. Postnatal depression and puerperal psychosis are two disorders most commonly associated with the perinatal period: the first, because of its high prevalence, 13% in the first few months following birth, the second because of its potentially disastrous consequences, including suicide, neglect of the baby and infanticide. [With external links to the current evidence base]

With a 10.5% lifetime risk, self-reported self-harm is common in the community: 5.6% have made a suicide attempt. Self-harm without lethal intent is slightly less common at 4.9%. Following an episode of self-harm the GP can offer assessment and practical support, for example, monitoring type and quantity of medication prescribed, and signposting or referral where relevant. GPs are ideally placed to support patients and their families following self-harm through an understanding and nonjudgmental approach which aims to alleviate distress.

Adults in the UK with a diagnosis of either ICD-10 depressive episode or ICD-10 mixed anxiety and depressive disorder have been estimated to have taken more than a quarter of the total number of days of sickness absence in one year. Few patients receive effective treatment. There are four reasons for this: failure to seek help (40% don't attend); failure of GPs to recognise depression (30-50% of cases); non-adherence or early cessation of treatment (only about 25% of patients complete a six-month course of antidepressant treatment);lack of treatment efficacy (50% with moderate depression don't respond to initial treatment). Only about one in ten patients receive effective treatment.

Psychosis is broadly defined as the presence of delusions and hallucinations and can be organic or functional in nature. The former is secondary to an underlying medical condition, such as delirium or dementia, the latter to a psychiatric disorder, such as schizophrenia or bipolar disorder. Functional psychosis is relatively common in the general population, with epidemiological studies estimating its prevalence to be approximately 0.2-0.7%. Prevalence in the elderly increases to 4.8%. The identification and treatment of psychosis is important as it is associated with a 10% lifetime risk of suicide and significant social exclusion. Delays in recognition can ultimately lead to a worse prognosis.

GPs play a crucial role in identifying patients who may be suffering from borderline personality disorder (BPD). All practitioners caring for patients with BPD  should work together in order to understand needs and risks and to provide patients with consistent support and help.BPD is associated with significant impairment of psychological, social and occupational functioning, with a suicide rate of almost 10%, a rate 50 times higher than in the general population.

In bipolar disorder patients are intermittently severely ill and unable to function, but they usually return to their normally functioning self. The extremes of symptoms and experiences require intensive specialist care,  but the overall success of management will depend on an informed and complementary interaction between primary and secondary care. Bipolar disorder is at least twice as common as schizophrenia, and eminently treatable. It is perfectly suited to the well established outpatient model practised in general practice.

Only a small minority of patients receive effective treatment for depression. About 40% of patients do not seek medical help, and of those who do, between 30 and 50% are not recognised as being depressed, usually as a result of somatic presentations. Patients may not be offered the appropriate treatment if strict diagnostic criteria are not applied, and under half of those receiving treatment will complete a minimal treatment course.

In recent decades the care of people with schizophrenia has shifted from hospital to the community. The GP's role has thus expanded, a fact reflected by the emphasis placed on primary care involvement in the recently updated NICE guideline on schizophrenia. On average GPs in the UK will have 7-12 people with schizophrenia on their lists, and for some of these patients they may be the sole provider of care.