Mood Disorders — Depression, Bipolar Criteria and Lithium

Mood is the sustained emotional background against which a person experiences life. A mood episode changes more than whether somebody feels happy or sad: sleep, energy, concentration, activity, appetite and judgement may all change. The diagnosis depends on the symptom pattern, duration, effect on functioning and lifetime history. A single observation of tearfulness or excitement cannot establish a mood disorder.

A major depressive episode can occur in both unipolar and bipolar illness. The depressive symptoms themselves do not reliably establish which illness is present. Before diagnosing major depressive disorder, ask specifically about earlier periods of unusually increased energy, reduced need for sleep, excessive activity and altered judgement. Collateral information from relatives or previous treatment records may reveal episodes that the patient regarded as productive rather than pathological.

The central exam distinction is between an episode and a disorder. An episode describes the current syndrome; a disorder describes the longitudinal pattern. A person currently depressed who previously had mania has bipolar I disorder. A person with hypomania and a major depressive episode, but no mania, has bipolar II disorder. Periods of normal mood between episodes do not cancel either diagnosis.

Using DSM-5-TR criteria, at least five symptoms must occur during the same two-week period, representing a change from previous functioning. At least one must be depressed mood or loss of interest or pleasure. The syndrome must cause clinically significant distress or impairment and should not be explained by a substance or another medical condition. In children and adolescents, irritable mood may substitute for depressed mood.

SIGECAPS is a memory aid for sleep, interest, guilt, energy, concentration, appetite, psychomotor change and suicidality. Add depressed mood to reconstruct the full symptom list. It is a recall aid rather than a scoring rule. Appetite loss and weight loss belong to the same symptom domain; similarly, insomnia and hypersomnia are alternatives within the sleep domain. Counting both separately can falsely create the required symptom total.

Assess the depressive syndrome and safety together. Ask about suicidal thoughts, intent, planning, access to means, previous attempts and available support. A patient can need urgent intervention even before the usual duration threshold is reached. A screening questionnaire can identify a need for assessment or follow change, but it does not replace a clinical interview or the exclusion of bipolar illness.

Both episodes require abnormally elevated, expansive or irritable mood and increased activity or energy. The associated symptoms are grandiosity, decreased need for sleep, pressured speech, racing thoughts or flight of ideas, distractibility, increased goal-directed activity or agitation, and risky activities. At least three associated symptoms are required, or four when the mood is only irritable. Irritability alone is therefore insufficient.

Reduced need for sleep means sleeping little while still feeling rested or energetic. It differs from insomnia in depression, where the patient wants to sleep and often feels tired. Grandiosity can range from unrealistic confidence to delusional beliefs in mania. Pressured speech is difficult to interrupt; flight of ideas describes rapid transitions between thoughts with associations that can still be followed.

The duration exception is specifically tied to hospitalization being necessary. Avoid casually dropping every duration requirement merely because a symptom is dramatic. At the same time, psychosis excludes hypomania, and dangerous behaviour requires prompt assessment. The episode must also be distinguished from stimulant intoxication, corticosteroid effects, thyroid dysfunction and other medical or neurological causes.

A manic episode is sufficient for bipolar I after the relevant exclusions. A history of alternating mania and depression is common, but the word alternating is not a mandatory diagnostic requirement. Bipolar II is not simply bipolar I with less severe depression. The distinction rests on the elevated episode: hypomania rather than mania. Depressive episodes in bipolar II may be severe and disabling.

Cyclothymia has numerous periods of hypomanic and depressive symptoms that fall below full episode criteria. The pattern lasts at least two years in adults, or one year in children and adolescents, occurs for at least half the time, and has no symptom-free interval longer than two months. These longitudinal requirements distinguish cyclothymia from ordinary short-term mood changes.

Rapid cycling counts qualifying episodes rather than daily emotional swings. Episodes are separated by remission or a switch in polarity. Mixed features describe simultaneous symptoms of opposite polarity within an episode and should not be confused with rapid cycling. In a vignette, first identify the current episode, then the lifetime disorder, and only then add a relevant course or episode specifier.

Obtain a timeline of symptoms rather than relying on the presenting complaint. Ask when the change started, how sleep and activity changed, whether work or relationships were disrupted, and whether the patient has experienced similar episodes. Review medications, recreational drugs, alcohol use and relevant physical symptoms. New mood symptoms in an unusual clinical context should prompt consideration of a medical or medication-related cause.

A mental state examination evaluates mood, affect, speech, thought form, thought content, perception, cognition, insight and judgement. In mania, risky spending or sexual behaviour may expose the patient and others to harm. In depression, psychomotor slowing and withdrawal may obscure suicidal intent. Risk assessment therefore includes self-harm, harm to others, self-neglect, vulnerability and the ability to maintain nutrition and hydration.

Psychotic symptoms do not automatically imply schizophrenia: severe depression and mania can both include psychosis. The relationship between psychosis and mood episodes, together with the longitudinal history, determines the differential. ADHD usually produces a persistent pattern rather than a distinct new episode of elevated mood and energy. Personality-related emotional changes can be reactive and brief, making the time course especially useful.

Treatment depends on severity, safety, previous response, comorbidity and patient preference. For unipolar depression, psychological therapies and antidepressants are established options. More severe depression often needs combined treatment. Psychotic depression, catatonia, acute suicidal risk or inability to maintain intake may require urgent specialist care; electroconvulsive therapy is an option when rapid improvement is needed or other treatments have failed.

Acute mania may require hospitalization, particularly with severe impairment, psychosis or dangerous behaviour. Antipsychotics and mood stabilizers such as lithium are important treatment options, and combinations may be used in severe illness. Lithium has a central place in relapse prevention, but the phrase drug of choice should not erase the immediate need to control agitation, assess physical health and protect the patient.

NICE lists quetiapine or the combination of fluoxetine with olanzapine among options for moderate or severe bipolar depression in an untreated patient. Lamotrigine has a role in selected bipolar depressive or maintenance settings but is not an acute antimanic treatment. Antidepressant monotherapy can destabilize bipolar I illness. Medication choice must distinguish treatment of the current episode from long-term prevention.

Lithium has a narrow therapeutic index and is eliminated through the kidneys. Its precise mood-stabilizing mechanism is not fully established; effects on intracellular signalling, including the phosphatidylinositol second-messenger system, are important pharmacology associations. A fixed tablet dose cannot guarantee a safe concentration because renal function, hydration, sodium balance and interacting medicines change lithium handling.

Before starting lithium, assess renal function, electrolytes including calcium, thyroid function, weight and relevant cardiovascular or pregnancy considerations. Serum sampling must be timed as a trough, with StatPearls describing eight to twelve hours after the latest dose. A sample taken soon after ingestion should not be interpreted as though it were a correctly timed trough. Repeat levels after initiation and dose changes according to the monitoring plan.

Targets vary by guideline and treatment phase. NICE recommends 0.6–0.8 mmol/L for people prescribed lithium for the first time, and consideration of 0.8–1.0 mmol/L in selected patients with previous relapse or persisting subthreshold symptoms. These are contextual targets, not universal boundaries separating safety from toxicity. Follow the clinical picture as well as the measured concentration.

• Monitor serum lithium together with renal function, thyroid function and calcium.
• Check hydration and changes in renal function during vomiting, diarrhoea, fever or excessive sweating.
• Review thiazide diuretics, NSAIDs and renin–angiotensin system antagonists, which can raise lithium levels.
• Explain the need for monitoring and a consistent fluid and salt intake.

Common associations include tremor, gastrointestinal symptoms and weight gain. Important longer-term effects are hypothyroidism or goitre, nephrogenic diabetes insipidus, and hyperparathyroidism with hypercalcaemia. Polyuria and polydipsia suggest impaired renal concentrating ability. These effects explain why follow-up must include organs affected by treatment, rather than measuring lithium alone.

Toxicity becomes increasingly likely above about 1.5 mmol/L, and levels above about 2.0 mmol/L are associated with severe neurological toxicity. Suspect toxicity when gastrointestinal illness occurs with worsening tremor, ataxia, confusion or other neurological changes, especially after dehydration or a new interacting drug. Stop lithium and arrange urgent clinical assessment. Management includes renal and electrolyte evaluation, appropriately monitored fluid treatment and specialist advice. Severe poisoning may need haemodialysis; dialysis decisions depend on symptoms, renal function and exposure pattern as well as concentration.

Pregnancy requires individual specialist risk–benefit assessment. Lithium exposure is associated with an increased risk of fetal cardiac malformations, including the classic Ebstein anomaly association. Avoid interpreting this as an instruction for abrupt unsupervised discontinuation: relapse also has consequences, and treatment and monitoring need a coordinated plan. Similarly, a fine tremor alone should not be treated as proof of life-threatening toxicity.