Classification & Assessment in Psychiatry · Paper A
Classification of movement disorders
Every abnormal movement in psychiatry sorts into one of a handful of named patterns, and the pattern — not the drug the patient happens to be on — tells you what is actually wrong. A tremor, a chorea, a dystoniaInvoluntary muscle contractions causing abnormal, sometimes painful, postures or movements.Read more →, a myoclonic jerk, a tic, akathisiaAn inner restlessness and urge to keep moving, a common side effect of antipsychotic drugs.Read more → and tardive dyskinesia can all look, at a glance, like 'the patient is moving strangely', but each is a different kind of breakdown in the brain's movement-gating system, and mixing them up means treating the wrong problem with the wrong fix.
⚠️ Treating any restless, pacing patient on an antipsychotic as worsening psychosis and raising the dose — if it is akathisiaAn inner restlessness and urge to keep moving, a common side effect of antipsychotic drugs.Read more →, a higher dose makes the restlessness worse, not better.
⚠️ Assuming tardive dyskinesia should improve when the causative drug's dose is lowered — the exam-defining feature is that it can do the opposite and become more obvious.
⚠️ Calling every oro-facial or limb movement in a patient on an antipsychotic 'tardive dyskinesia' without checking the timeline — the same movement quality within hours to weeks of starting treatment is far more likely to be acute dystoniaInvoluntary muscle contractions causing abnormal, sometimes painful, postures or movements.Read more → or drug-induced parkinsonism.
⚠️ Missing that a movement disorder does not need a drug at all — essential tremor, Huntington's chorea and Tourette syndrome all occur with no antipsychotic in sight, and family history is often the detail that reveals it.
⚠️ Reading fever plus rigidity in a patient on an antipsychotic as automatically neurolepticAnother word for an antipsychotic drug.Read more → malignant syndrome without checking the timescale and reflexes — a slower, hyporeflexic picture over days points to NMSNeuroleptic malignant syndrome, a rare, dangerous reaction to antipsychotic medication causing fever and muscle rigidity.Read more →, while a fast, hyperreflexic, clonusRhythmic, involuntary muscle contractions, often tested at the ankle.Read more →-positive picture within hours points to serotonin syndromeA dangerous reaction from too much serotonin activity, causing agitation, high temperature, and muscle overactivity.Read more → instead.
Imagine three patients waiting in the same clinic. One's hand won't stop trembling. Another's face keeps twisting into strange shapes she can't control. A third can't sit still in her chair, rocking and pacing no matter how hard she tries to hold still. All three would be called, loosely, "a movement disorder" — but they are three completely different problems, made by different mechanisms, needing different treatments, and confusing them is one of the most common ways a psychiatric case gets got wrong. This page builds, from nothing, the vocabulary and the rules that let you tell one abnormal movement from another, a skill you will use every week on the ward, because the drugs psychiatry relies on most heavily — antipsychotics — are themselves one of the biggest causes of abnormal movement in medicine.
A movement disorder is any condition in which the body produces movement that is either too much (called hyperkinetic — extra, unwanted movement appearing on top of normal activity) or too little (called hypokinetic — movement that is slow, reduced, or hard to start). That single split is the first and most useful sorting question you can ask about any abnormal movement you see. Chorea, , , tics, and tardive dyskinesia all belong on the too-much side. Parkinsonism (slowness, stiffness and tremor together) belongs on the too-little side, even though it includes a tremor — which shows you that these two categories are not simply about how much a body part moves overall, but about the specific kind of extra or missing movement being produced.
Here is the trap almost every learner falls into: assuming that being on an antipsychotic automatically means a movement is drug-induced, and that the only job is to spot the movement and blame the tablet. In reality the exact same movement can be caused by a drug in one patient and by a completely separate, unrelated neurological illness in another — a tremor can be essential tremor (inherited, nothing to do with any medicine) or it can be caused by lithium; a chorea can be Huntington's disease (an inherited brain illness) or, rarely, follow a drug.
What actually separates a drug cause from a primary neurological cause is not the movement itself but its timing (did it start soon after a dose change?), its direction of change with dose (does it get better or worse when the dose is lowered?), and the wider picture (family history, other neurological signs). Skipping straight from movement-plus-antipsychotic to drug-induced, without checking these three things, is the single most common way this topic is answered wrong.
Voluntary movement in a healthy nervous system depends on a loop running through the (a cluster of connected structures deep in the brain that fine-tunes and releases movement, acting like a gatekeeper that lets a wanted movement through while holding back everything unwanted) and its chief chemical messenger, dopamine. When that gatekeeper works normally, you move exactly what you intend, exactly when you intend it, and nothing else. Every movement disorder in this topic is what happens when some part of that gatekeeping breaks in a specific, recognisable way.
Block dopamine too hard, which is exactly what every antipsychotic does, and the gatekeeper becomes over-strict: wanted movement gets held back too, producing the slowness and stiffness of parkinsonism, or a spasm forces its way through unpredictably as acute . Let a movement-generating circuit fire in an uncoordinated, flowing way instead, and you get chorea. Let the gate fail to hold a sustained wrong signal, and a muscle group locks into an abnormal posture — dystonia again, but now a chronic pattern rather than a single spasm. Damage the fastest, most reflexive layer of that same system and you get , a shock rather than a spasm. Each named movement disorder is not an arbitrary label; it is what a specific kind of breakdown, at a specific point in one shared circuit, looks like from the outside.
You separate one movement disorder from another the same way every time, by asking four questions in order, and each answer narrows the list.
First: is it rhythmic? A tremor is a regular back-and-forth oscillation, like a metronome, for example around four to six beats a second. Nothing else on this list is rhythmic in that way; chorea, and tics are all irregular.
Second: how long does each movement last? is a shock — a single, very brief jerk, over almost as soon as it starts. Chorea is longer and flows: one movement blends into the next, migrating from one body part to another, like a slow-motion dance the patient never chose. lasts longest of all: a sustained contraction that can hold a limb or the neck in an abnormal posture for seconds, minutes, or, in a chronic form, indefinitely.
Third: can the patient stop it? A tic is unique on this list for being briefly, voluntarily suppressible — the patient can hold it back for a few minutes, at the cost of a mounting inner tension (a premonitory urge) that is relieved the moment the tic is finally let out. Nothing else here can be voluntarily switched off, even briefly.
Fourth: is there a felt urge driving it? is defined as much by what the patient feels, an unbearable inner restlessness, as by what you see: pacing, rocking, foot-shifting. Imagine trying to sit through a two-hour exam with an itch you can never fully scratch, except the itch is a to move your whole body. That subjective half is what separates akathisia from simple agitation.
Run a patient's movement through these four questions and you will land on the right name almost every time.
| Movement | Speed / pattern | Suppressible? | Classic antipsychotic timing |
|---|---|---|---|
| Tremor | Rhythmic oscillation | No | Variable; parkinsonism's tremor: days-weeks |
| Chorea | Irregular, flowing, migrates | No | Rare as a drug effect; classically Huntington's |
| (acute) | Sustained abnormal posture | No, resisted | Hours after dose start or rise |
| Sudden, brief, shock-like | No | Not typical; consider metabolic/ cause | |
| Tics | Brief, stereotyped, repeated | Briefly, rising tension | Not drug-related; childhood onset |
| Restlessness, urge plus pacing | No | Days to weeks after dose change | |
| Tardive dyskinesia | Oro-facial chewing, sometimes limb chorea | No | Months-years; may worsen on lower dose |
There is no blood test or scan that names a movement disorder for you; the diagnosis rests on careful bedside observation, using the four questions from the walk-through above, together with the history — what drug the patient is on, when it was started or last changed, and whether anyone in the family has had a similar illness. A few extra checks matter for specific look-alikes: a raised creatine kinase (a blood test for muscle breakdown) alongside fever and rigidity should make you screen urgently for malignant syndrome rather than simple drug-induced parkinsonism, and a genetic test for the Huntington's disease gene expansion can confirm chorea's cause once the family history and examination point that way. Investigation, in other words, is used to confirm a serious look-alike or an inherited cause; the everyday differential is made by watching the movement itself.
Management follows directly from getting the classification right, because each category responds to a different fix, and treating one as if it were another can make things worse — this is exactly the kind of drug-induced movement problem the Maudsley Prescribing Guidelines in Psychiatry, the standard UK prescribing reference, sets out specific advice on. Acute is a same-day emergency: an drug (procyclidine, given intramuscularly if needed) reverses it within minutes by restoring the balance the antipsychotic disturbed.
Drug-induced parkinsonism and are treated by first lowering the causative dose or switching to a lower- antipsychotic; akathisia can also respond to a beta-blocker such as propranolol. What must never happen, and this is the exam's favourite trap, is simply raising the antipsychotic dose — that is what happens when akathisia is mistaken for worsening psychotic agitation, and it only makes the restlessness worse.
Tardive dyskinesia is the hardest of the group to manage. Options include stopping or reducing the causative drug where possible (recognising it may briefly worsen first), switching to a lower-risk antipsychotic such as clozapine, or adding a specific drug that reduces the abnormal movements directly. Because it can be irreversible, the real management is prevention: use the lowest effective antipsychotic dose for the shortest necessary time, and examine every patient regularly for early signs, catching it before it becomes established.
Chorea, and tics, when caused by a primary neurological or genetic illness rather than a drug, are managed differently again: by treating the underlying cause and, where needed, a specific movement-suppressing medication chosen for that condition — a pathway with nothing to do with adjusting an antipsychotic dose.
The vignette will describe a movement and expect you to name it purely from its phenomenology, rhythmic or not, brief or sustained, suppressible or not, felt as an urge or not, often before it even tells you which drug the patient is on. The classic trap pairs with a dose increase: a restless, pacing patient is read as "more agitated psychosis" and given more antipsychotic, which only deepens the restlessness. Before you move on, test yourself: could you explain to a friend, using only those four questions, why chorea and tardive dyskinesia's tongue movements can look alike on a video yet are told apart by the drug history and the direction of the dose-response?
Classify any abnormal movement by four questions, rhythmic, brief-or-sustained, suppressible, urge-driven, before you ever ask which drug the patient is on, because those same four questions separate a genuine drug-induced emergency from a primary neurological illness that a dose change will never fix.