6.3.1 Psychiatric assessment of patients with physical illness

The liaison assessment

A liaison assessment identifies the syndrome and its causes, the risks, any capacity questions, and the treatment or nursing changes that would help.

• Clarify the referral with the team first, because "assess mood" may mean depression, treatment refusal, confusion or a breakdown in communication.

• Review the observations, results and drug chart, including recent medication changes, before drawing conclusions.

• Take a collateral history when illness or sedation limits communication, and remember that curtains do not stop others hearing.

Delirium and cognition

• Assess attention, cognition and arousal against baseline, using a structured tool such as the 4AT alongside clinical assessment.

• Hypoactive delirium can look like depression, and delirium is easily missed in a patient who converses plausibly.

Differential diagnosis on the general ward

Physical illness can disturb sleep, appetite, energy and concentration without depression, so give weight to anhedonia, guilt, worthlessness, hopelessness and suicidal thinking.

These can coexist: delirium can complicate dementia or depression.

Risk and capacity

• A capacitous adult may refuse treatment, even life-saving treatment, and disagreement does not prove incapacity.

• Mental health detention does not generally authorise unrelated physical treatment.

Endocrine disorders that mimic psychiatric illness

• Addison's disease gives hyperkalaemia because aldosterone and cortisol are both lost; other endocrine and psychiatric mimics give a normal or low potassium.

• Pigmentation marks primary adrenal failure, because raised adrenocorticotropic hormone darkens the skin.

• Depression is the commonest psychiatric disorder in Cushing syndrome (chronic endogenous hypercortisolism), ahead of anxiety, mania, cognitive change and psychosis.

• Hypothyroidism affects about ten women for every man.

• Primary hyperparathyroidism is the commonest cause of hypercalcaemia outside hospital.

• Long-term lithium can cause parathyroid hyperplasia or adenoma, and a therapeutic lithium level does not exclude hypercalcaemia, so calcium is checked before and during treatment.

• Whipple's triad is symptoms, a low glucose during an attack, and relief with glucose.

Electrolytes and the heart

• Severe hyponatraemia is the common blood abnormality most likely to cause delirium in an older inpatient, unlike mild anaemia, mild hypokalaemia, slightly raised urea or low albumin.

• Psychogenic polydipsia in chronic schizophrenia dilutes serum sodium when intake exceeds renal free water excretion, giving weight gain across the day, then confusion, vomiting and seizures.

• Refeeding syndrome in a severely underweight patient causes hypophosphataemia, because insulin released by the carbohydrate load drives phosphate into cells.

• Refeeding syndrome gives confusion, breathlessness, oedema, weak painful muscles, cardiorespiratory failure and rhabdomyolysis.

• Hypocalcaemia prolongs the QT interval by lengthening the ST segment, whereas hyperkalaemia and hypercalcaemia leave it normal or short.

• Macrolide antibiotics prolong the corrected QT interval by blocking cardiac potassium channels; sertraline has little effect, unlike citalopram, whose effect is dose-related.

• Depression in heart failure is two to three times as frequent as in the general population, affecting about one patient in five.

Other physical illnesses that mimic psychiatric disorder

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• Porphyria attacks are provoked by oestrogens, fasting, alcohol and drugs such as carbamazepine.

HIV infection

• In untreated human immunodeficiency virus (HIV) infection with a low CD4 count, fever, subacute focal signs and multiple ring-enhancing lesions with oedema indicate cerebral toxoplasmosis rather than lymphoma.

• Kaposi's sarcoma, a vascular tumour driven by human herpesvirus 8, appears in AIDS as painless violaceous macules, plaques and nodules on skin and oral mucosa, classically the hard palate.

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Liver disease

• Asterixis, a flap caused by lapses in postural tone, is the characteristic sign of hepatic encephalopathy.

• In significant hepatic impairment, choose lorazepam, oxazepam or temazepam, which are cleared by glucuronide conjugation to inactive metabolites.

• Conjugation is relatively spared in cirrhosis, whereas oxidative metabolism falls early and yields long-lived active metabolites.

• In severe hepatic impairment with encephalopathy risk, sulpiride is the preferred antipsychotic, because this benzamide is excreted largely unchanged by the kidneys and causes little sedation or constipation.

Brain imaging

• The one practical advantage of magnetic resonance imaging (MRI) over computed tomography (CT) is no ionising radiation; speed, cost, tolerance in claustrophobia and metal safety all favour CT.

• When an implant or ferromagnetic body rules out MRI, request CT to exclude an intracranial cause of delirium, because SPECT, PET and MR spectroscopy are functional or metabolic studies.

Medically unexplained and simulated presentations

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