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Frontal lobe dysfunction is not one illness — it is at least three separate wiring faults that happen to share an address. A dorsolateral fault produces apathy that looks like depression. An orbitofrontal fault produces impulsivity that looks like maniaA period of abnormally elevated mood, energy and activity, seen in bipolar disorder.Read more →. A medial fault produces frozen silence that looks like catatoniaA syndrome of abnormal movement and behaviour, ranging from being frozen and unresponsive to being excessively agitated.Read more →. The exam question is almost never 'is this frontal' — it is 'which wiring fault, and which look-alike is it not'.

• The frontal lobesThe front part of the brain, involved in planning, personality and impulse control.Read more → run three largely separable circuits, each producing its own signature syndrome when damaged: DORSOLATERAL (planning, set-shifting, abstraction — the 'cold', formally-tested side), ORBITOFRONTAL (impulse control, social judgement — the 'hot' side), and MEDIAL/anterior cingulate (drive and initiation).
• Dorsolateral damage produces apathy, poor planning and perseverationPersistently repeating a word, phrase, or action after it is no longer relevant or has already been asked for.Read more →, but social conduct is relatively preserved — this is the pattern most easily mistaken for depression.
• Orbitofrontal damage produces disinhibition, tactlessness and poor judgement, often with entirely normal formal test scores (a normal card-sorting result does not exclude it) — this is the pattern most easily mistaken for maniaA period of abnormally elevated mood, energy and activity, seen in bipolar disorder.Read more → or a primary personality change.
• Medial/anterior cingulate damage produces akinetic mutismA complete absence of speech despite the physical ability to speak.Read more →: profound loss of drive to move or speak, in a patient who is awake and can still visually track — this is the pattern most easily mistaken for catatoniaA syndrome of abnormal movement and behaviour, ranging from being frozen and unresponsive to being excessively agitated.Read more → or reduced consciousness.
• Beyond focal lesions, several other conditions produce a frontal-looking picture through a different mechanism entirely. These include frontotemporal dementia (progressive neurodegeneration of the same circuits), alcohol-related brain damage (thiamine-deficiency injury that also devastates memory circuits, producing Korsakoff syndromeA chronic memory disorder, usually from thiamine deficiency, marked by severe short-term memory loss and confabulation.Read more →), and normal pressure hydrocephalus (mechanical ventricular pressure on frontal-subcortical white matterBrain tissue made mostly of the insulated, myelin-covered wires connecting nerve cells.Read more →).
• Because several of these mimics are themselves primarily psychiatric (maniaA period of abnormally elevated mood, energy and activity, seen in bipolar disorder.Read more →, depression, personality disorder, catatoniaA syndrome of abnormal movement and behaviour, ranging from being frozen and unresponsive to being excessively agitated.Read more →), the discriminating feature is rarely the frontal-looking behaviour itself. It is the course (acute versus chronic versus episodic), the associated features (a mood-episode history, an amnestic gap, a gait or continence change), and whether the change is new or lifelong. In practice, this is why the vignette's course and associated features carry more diagnostic weight than the frontal-looking behaviour itself.

• A vignette describing apathy plus poor planning, with no mood-episode history and no subjective distress, after a defined structural insult, is describing dorsolateral frontal dysfunction, not depression.
• A vignette describing disinhibition and poor judgement with NORMAL formal test performance is describing orbitofrontal syndrome — normal test scores do not rule this out.
• A vignette describing an awake patient who tracks visually but does not speak or move, with NO waxy flexibilityA catatonic sign where a limb, moved into a position by someone else, stays there as if made of soft wax.Read more → or posturing, is describing medial-frontal akinetic mutismA complete absence of speech despite the physical ability to speak.Read more →, not catatoniaA syndrome of abnormal movement and behaviour, ranging from being frozen and unresponsive to being excessively agitated.Read more →.
• A vignette describing progressive disinhibition or ritualistic behaviour over months to years with preserved memory testing is describing behavioural variant frontotemporal dementia.
• A vignette pairing frontal-executive impairment with a disproportionate anterograde amnesia and confabulationFilling a gap in memory with a made-up answer the person genuinely believes is true, not a deliberate lie.Read more → is describing Korsakoff syndromeA chronic memory disorder, usually from thiamine deficiency, marked by severe short-term memory loss and confabulation.Read more →, not a pure frontal syndrome.
• A vignette pairing executive slowing with a gait change and urinary incontinence is describing normal pressure hydrocephalus.

• Dorsolateral syndrome vs depression (pseudodementia) — both apathetic and poor on effortful testing; depression has an episodic mood-disorder history, distress, and improves when mood is treated, while a structural dorsolateral syndrome is stable and often unaccompanied by subjective distress.
• Orbitofrontal syndrome vs maniaA period of abnormally elevated mood, energy and activity, seen in bipolar disorder.Read more → — both disinhibited and impulsive; mania is episodic and tied to elevated/irritable mood, reduced sleep need and grandiosity, usually with a prior mood-episode history, while orbitofrontal syndrome follows a specific lesion and is not mood-episodic.
• Orbitofrontal syndrome vs antisocial personality disorder — both show disregard for social norms; personality disorder is a lifelong, stable pattern from adolescence, while orbitofrontal syndrome is a NEW change from a previous baseline after a defined insult.
• Medial frontal akinetic mutismA complete absence of speech despite the physical ability to speak.Read more → vs catatoniaA syndrome of abnormal movement and behaviour, ranging from being frozen and unresponsive to being excessively agitated.Read more → — both immobile and mute; catatonia adds positive motor signs (waxy flexibilityA catatonic sign where a limb, moved into a position by someone else, stays there as if made of soft wax.Read more →, posturing, negativismResisting or doing the opposite of what is asked, without any apparent reason.Read more →, mitgehen) and usually has an underlying psychiatric or medical illness, while akinetic mutism is a pure loss of initiation with no positive motor signs.
• Behavioural variant frontotemporal dementia vs late-onset primary psychiatric change — bvFTD is progressive over months to years, precedes memory loss, and eventually shows frontotemporal atrophy on imaging, while a primary psychiatric change is more often episodic or has a clear precipitant.
• Alcohol-related brain damage/Korsakoff vs a pure frontal syndrome — both show executive impairment, but Korsakoff's anterograde amnesia and confabulationFilling a gap in memory with a made-up answer the person genuinely believes is true, not a deliberate lie.Read more → are disproportionate to everything else, which a pure frontal syndrome does not produce.
• Normal pressure hydrocephalus vs dorsolateral syndrome — both produce executive slowing; NPH adds the gait-apraxia-plus-incontinence triad and disproportionate ventriculomegaly on imaging.

• ⚠️ Calling any apathetic, poorly-performing patient 'depressed' or any disinhibited patient 'manic' without checking course and associated features — the single highest-yield trap across this whole topic.
• Assuming a normal formal executive test (card-sorting) excludes frontal dysfunction — it specifically does not for orbitofrontal syndrome, which classically spares those tests.
• Mistaking akinetic mutismA complete absence of speech despite the physical ability to speak.Read more → for a reduced level of consciousness — the patient is awake and visually tracks; treating it as coma-spectrum leads to the wrong work-up.
• Mistaking akinetic mutismA complete absence of speech despite the physical ability to speak.Read more → for catatoniaA syndrome of abnormal movement and behaviour, ranging from being frozen and unresponsive to being excessively agitated.Read more → because both are immobile and mute — only the presence of positive motor signs (waxy flexibilityA catatonic sign where a limb, moved into a position by someone else, stays there as if made of soft wax.Read more →, posturing, negativismResisting or doing the opposite of what is asked, without any apparent reason.Read more →) earns the catatonia label.
• Forgetting that antisocial personality disorder requires a LIFELONG pattern — labelling a genuinely new post-lesion behaviour change as a personality disorder misses the acquired brain injury.
• Anchoring on 'frontal lobeThe front part of the brain, involved in planning, personality and impulse control.Read more →' as a single undifferentiated diagnosis rather than naming which of the three sub-syndromes the vignette is actually describing.

• First localise, is the described behaviour apathetic/poor-planning (dorsolateral), disinhibited/impulsive (orbitofrontal), or frozen/mute (medial)? Name the sub-syndrome before reaching for a mimic.
• Then check course, acute and fluctuating points to delirium; episodic and mood-linked points to maniaA period of abnormally elevated mood, energy and activity, seen in bipolar disorder.Read more → or depression; lifelong and stable points to a personality disorder; progressive over months to years points to a dementia process.
• Then check for a disqualifying extra feature that rules OUT the frontal-only explanation: a gait/continence triad (normal pressure hydrocephalus), disproportionate amnesia with confabulationFilling a gap in memory with a made-up answer the person genuinely believes is true, not a deliberate lie.Read more → (Korsakoff), or positive catatonic motor signs (catatoniaA syndrome of abnormal movement and behaviour, ranging from being frozen and unresponsive to being excessively agitated.Read more →).
• If formal executive testing is reported as normal, do not use that to exclude orbitofrontal syndrome — check instead whether the social/behavioural description alone is diagnostic.
• If the patient is immobile and mute, check specifically for wakefulness and visual tracking (present in akinetic mutismA complete absence of speech despite the physical ability to speak.Read more →, and usually absent or different in reduced consciousness) before naming either catatoniaA syndrome of abnormal movement and behaviour, ranging from being frozen and unresponsive to being excessively agitated.Read more → or a conscious-level problem.