7. Psychosis as a Syndrome: "why is this patient psychotic?"

The reasoning

Psychosis = a syndrome of impaired reality testing (positive symptoms: hallucinations, delusions, disorganisation; and/or negative symptoms: blunting, avolition, alogia, asociality, anhedonia). It is emphatically not synonymous with schizophrenia. The disciplined move is to run an ordered differential, organic causes first because they're time‑critical and reversible:

1. Delirium / organic — fluctuating consciousness, inattention, visual hallucinations, acute onset. Screen: infection, metabolic (Na⁺, Ca²⁺, glucose, uraemia, hepatic), hypoxia, thyroid, B12, autoimmune/limbic encephalitis (esp. young, rapid, with seizures/movement disorder/dysautonomia), CNS lesion, epilepsy, HIV/neurosyphilis.
2. Substance‑induced — intoxication (stimulants, cannabis/synthetics, hallucinogens) or withdrawal (alcohol, sedatives). Use the timeline principle: symptoms tied to use/cessation and resolving with abstinence.
3. Medication‑induced — steroids, dopaminergics, anticholinergics, stimulants.
4. Affective psychosis — mood‑congruent psychosis within a depressive or manic episode (treat the mood disorder).
5. Primary psychotic disorder — schizophrenia spectrum, schizoaffective, delusional disorder, brief psychotic disorder — a diagnosis of exclusion and duration.

"Why is this patient psychotic?" — the ordered differential as a decision tree:

The workup this differential demands

Collateral history; MSE with consciousness + cognition; vitals; bloods (FBC, U&E, Ca²⁺, glucose, LFTs, TFTs, B12/folate, CRP); toxicology; and, when features warrant (first episode with atypical/neurological signs, age extremes, rapid decline), neuroimaging + EEG ± LP/autoimmune antibodies.

Red flags that mandate an organic hunt 🚩

Acute onset · fluctuating consciousness · visual/olfactory/tactile hallucinations · disorientation/inattention · focal neurology, seizures, or abnormal movements · age <15 or >45 at first presentation · rapid cognitive decline · autonomic instability.

Pitfalls

• Anchoring on "schizophrenia" at first contact and missing delirium/encephalitis — the archetypal harmful error.
• Forgetting that negative symptoms can be the presenting picture and are easily mislabelled as depression or "poor motivation."

Pearls

• 🎯 Schizophrenia is a diagnosis of exclusion and time. Positive symptoms open the differential; duration + exclusion of mimics close it.
• 🩺 First‑episode psychosis with any neurological sign, catatonia, or a subacute confusional picture → think autoimmune encephalitis and escalate; it's treatable and missed.

Next → With the syndrome mapped, we go deep on its most important cause — schizophrenia — its core features, differential, pharmacology, and management (Part 2).