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Stroke Mimics And Chameleons

Learning objectives

  • Causes of Stroke Mimics
  • Investigations of mimics
  • Management of mimics


  • Mimics are conditions that at first assessment can include stroke within the differential.
  • Stroke mimics are medical conditions that look like strokes, while chameleons are strokes that look like other conditions
  • The diagnosis may become obvious very quickly or they may be admitted under the stroke team and the diagnosis made later.
  • Indeed I have seen some patients were for example seizure or tumour as the diagnosis was not apparent until some time later when readmitted with a similar presentation.
  • Often mimics can be thrombolysed as this is often done with limited information
  • Many mimics simply cannot be distinguished from stroke in the emergency setting when time is short to allow treatment.

Factors increasing likelihood of being stroke

Stroke mimics are medical conditions that look like strokes, while chameleons are strokes that look like other conditions

  • Sudden onset neurological deficit
  • Clear time of onset
  • Atrial fibrillation
  • Older age group
  • Hypertension, smoker, diabetes
  • Negative neurology
  • Pattern fits a stroke vascular syndrome

Things that look like but are not Strokes - "Mimics"

HypoglycaemiaAlways look for and treat hypoglycemia even in non diabetic patients. A low BM can mimic stroke. Always check pre hospital or in hospital and give glucose as is needed
Seizure (17%)Seizures which are unwitnessed resulting in a comatose patient being admitted with a possible unilateral weakness can often be directed to stroke team. If there is a clear history of seizure then the differentiation is easier. However some patients may be having a focal seizure with generalisation after an old stroke. Seizure is rare in the acute stroke setting. All should have a CT. Management will depend on findings. Stroke patients unless there is a catastrophic lesion which should be visible on CT should not be comatose with a few rare exceptions. Seziures can be left with a Todd's paresis which may last u to 72 hours and confusion which can last up to a week
Systemic infection/Sepsis (17%)Patients with old strokes who get sepsis or another metabolic disturbance may have return of their original stroke symptoms. I call these OSSIs "Ozzies" (Old Stroke Systemic illness). CT will typically show the old lesion. CRP /WCC may be elevated. Common in elderly patient. Often UTI or chest infections.
EncephalitisHSV encephalitis, other infections and Autoimmune. Pyrexia, headache, dysphasia if dominant temporal lobe. MRI suggestive, CSF and PCR diagnostic. Need Aciclovir immediately.
Brain tumour (15%)It is not uncommon and on going back over the story of the time of onset can be less clear. Patients may bleed into tumours with sudden worseningor the tumour may obstruct or compress vascular structures or cause a Todd's paresis. By the time that space occupying lesions become symptomatic they are often large and can be seen on CT. Single lesions can be primary brain or metastatic, multiple lesions tend to be metastases and patients need a full work up with CT with contrast or MRI with Gadolinium. If a metastatic lesion is considered then a CT Chest-abdomen and pelvis is needed and referral to neurosurgery and neuro-oncology. Steroids such as Dexamethasone may be started in the acute phase to reduce any vasogenic oedema. The imaging here shows a classical ring like appearance. The differential can always include an abscess.
Severe hyponatraemia Check U&E for other changes. One would expect a Na <120 mmol/L to cause neurological complaints. If above this look for other causes such as drugs, opiates.
Positional vertigo (6%) Isolated vertigo is more likely to be vestibular. Especially if positional or brought on by head movements and is intermittent. Stroke related vertigo is ongoing and usually accompanied by other brainstem signs.
Subdural haematoma Seen in older patients and those on anticoagulants. The CT is usually quite clear and again these tend to be large with symptoms which may even be transient and can be mistaken for TIA. Any anticoagulants or antithrombotic therapy must be stopped and patient discussed with Neurosurgeons. Usually surgery will be delayed if patient is well and normal GCS. Management is often conservative.
FunctionalPoorly understood. Very effortful attempts at movement with grunting and effort seemingly to little effect. Raise arm in air and let it drop in a controlled way and look for a catch of return of power. Tested together big difference in weakness but this is less clear when test each arm in turn with lots of encouragement. May be a disparity in weakness and functionality e.g. little power but can walk. Can be very convincing. May be funny walks which can be quite animated. The gait in someone at fear of falling is slow, wide based and holding on with the centre of gravity being kept as central as possible. Any great swaying movements where the COG seems to go wide of the trunk is not pathological especially if patient can recover and remain upright. Need expert diagnosis and experienced therapists often useful. Needs negative MRI if unsure.
MalingeringSome patients can act out a stroke in order to get a bed for the night or some other reason and are deliberately manipulative. There was a patient going around the country being thrombolysed in various centres. Once you can fake pronator drift and some weakness it is difficult to not take seriously initially and you will get a HASU bed. Never confuse with functional patients who need sympathy and support and reassurance and do not wish to be unwell and in hospital.
Bell's palsyCan be misdiagnosed as a stroke causing facial weakness. See relevant section for key signs
Alcohol intoxicationI have certainly thrombolysed a lady who was quite drunk and had an apparent arm weakness NIHSS 4 which resolved when she sobered up. MRI negative.
Migraine with unilateral motor weakness (MUMS)Recently been described and has similarities with functional. Imaging is normal, signs are variable. My own experience is of stuttering speech and tingling tongues and paraesthesias being useful pointers towards a more migraine variant type diagnosis. Very poorly understood.
Central pontine demyelination (myelinosis)Reduced level of consciousness and pinpoint pupils and quadriparesis often in setting of alcoholism and altered sodium levels usually from low to high with overcorrection of chronic hyponatraemia. Can be mistaken for a brainstem event. MRI is needed.
HypocalcaemiaGeneralised weakness + tetany especially when severe. May have associated tingling.
Foot dropUsually a common fibular (peroneal) nerve monoparesis
Acute disseminated encephalomyelitis (ADEM)Seizures, weakness, may be bilateral neurology - MRI is diagnostic. Neurology referral. May need LP and steroids
Multiple sclerosis (MS)Motor, sensory and other disturbance. Needs MRI and LP. Neurology referral. May need LP and steroids
Fractures Unilateral "hemiparesis" due to a fractured humerus and femur on the same side after a fall . Was referred to me by ED

Strokes Missed: Things that look like something else but are Strokes - "Chameleons"

The converse of the “stroke mimic” is a presentation suggestive of another condition, which actually represents stroke. These would be “stroke chameleons.” The recognition of a chameleon as stroke has implications for therapy and quality of care.

Acute DeliriumLeft hemisphere stroke with dysphasia
Cauda equina syndromeSpinal cord infarction
Monoparesis thought to be due to a MyelopathyFocal (ACA) Infarction in the C/L Motor cortex
SyncopeFound to be stroke
Hypertension emergencyFound to be stroke
Acute ataxia put down to alcoholPatient kept in police cells as ataxic and drunk was really an acute cerebellar infarct
Dizziness thought to be Vestibular neuronitisLateral medullary, lateral pontine and inferior cerebellar patterns of infarction may mimic the clinical features of vestibular neuronitis

References and further reading

Last updated: 14/11/2018

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