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Stroke Mimics And Chameleons

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Stroke Mimics and Chameleons

Introduction

Stroke mimics are conditions that resemble stroke at first assessment, while chameleons are strokes that present with atypical symptoms, making them appear as other conditions.
Initial diagnosis of a stroke mimic may not be immediately clear and can require further investigation, sometimes only diagnosed correctly after repeat admission or additional symptoms develop.
Due to the urgency of stroke treatment, some mimics may be thrombolysed before the true diagnosis becomes evident. Differentiating stroke from a mimic is challenging in an emergency setting.
Recognizing the features of mimics and chameleons is crucial for accurate diagnosis and management.

Factors Increasing Likelihood of Stroke

Certain features increase the likelihood that a condition is a true stroke rather than a mimic:

Sudden onset of neurological deficit
Clear time of onset
Presence of atrial fibrillation
Older age group
Risk factors like hypertension, smoking, and diabetes
“Negative neurology” with no additional systemic symptoms
Pattern consistent with a stroke vascular syndrome

Common Stroke Mimics

Conditions that can resemble strokes, requiring careful evaluation:

Mimic	Details
Hypoglycaemia	Hypoglycemia can mimic stroke, even in non-diabetic patients. Always check blood glucose and correct hypoglycemia urgently.
Seizure (17%)	Post-seizure weakness (Todd's paresis) can resemble stroke. History of seizures helps differentiate, but unwitnessed seizures may lead to initial stroke misdiagnosis. CT is necessary; Todd’s paresis may last up to 72 hours.
Systemic infection/Sepsis (17%)	Old stroke patients may experience "Old Stroke Systemic Illness" (OSSI), presenting as transient stroke-like symptoms. Check for UTI, respiratory infections, and elevated CRP/WCC. CT typically shows old lesions.
Encephalitis	Infections like HSV or autoimmune encephalitis can present with fever, headache, and confusion. MRI and CSF analysis, with PCR for viral detection, are essential. Aciclovir is used in suspected HSV cases.
Brain Tumor (15%)	Tumors can mimic strokes, especially if they bleed or compress vascular structures. A detailed history often reveals a gradual onset. Imaging (MRI with gadolinium) can confirm the diagnosis. Steroids may reduce cerebral edema.
Severe Hyponatraemia	Severe sodium depletion (Na <120 mmol/L) can cause neurological symptoms. Sodium correction is essential; symptoms may resolve with treatment.
Positional Vertigo (6%)	Benign positional vertigo is typically positional and transient. Persistent vertigo with brainstem signs suggests a possible stroke.
Subdural Hematoma	Common in older adults, especially on anticoagulants. CT imaging shows the hematoma clearly. Symptoms can be subtle and may mimic TIA or stroke.
Functional Disorders	Functional weakness can be difficult to distinguish from stroke. Look for signs like inconsistent effort, exaggerated movements, and discrepancies in weakness. MRI can help exclude organic pathology.
Malingering	Rare but possible; patients may simulate stroke symptoms for secondary gain. Professional observation can help identify malingering, which differs from functional disorders in intent.
Bell's Palsy	Can be mistaken for stroke if facial weakness is prominent. Check for forehead sparing, which is typical of central facial weakness in stroke.
Alcohol Intoxication	Alcohol can impair consciousness and cause limb weakness. Patients with high alcohol levels should be re-assessed when sober if initial imaging is negative.
Migraine with Unilateral Motor Weakness (MUMS)	This migraine variant can mimic stroke with symptoms like speech disturbances and unilateral weakness. MRI is typically normal.
Central Pontine Myelinolysis	Presents with altered consciousness, quadriparesis, and pinpoint pupils, often due to rapid correction of chronic hyponatremia. MRI is diagnostic.
Hypocalcemia	Severe hypocalcemia causes tetany and generalized weakness, which may resemble stroke. Serum calcium assessment is essential.
Foot Drop	Usually caused by common fibular (peroneal) nerve injury rather than a central lesion. Careful neurological examination can differentiate.
Acute Disseminated Encephalomyelitis (ADEM)	May cause bilateral neurological signs and mimic stroke. MRI and lumbar puncture are required; steroids may be used for treatment.
Multiple Sclerosis (MS)	MS flare-ups can resemble stroke. Diagnosis requires MRI, possibly with lumbar puncture for oligoclonal bands.
Fractures	Trauma-related fractures (e.g., humerus, femur) may cause unilateral immobility, mimicking hemiparesis. Imaging clarifies the diagnosis.

Stroke Chameleons: Strokes that Mimic Other Conditions

Stroke chameleons are true strokes presenting with atypical symptoms that resemble other conditions. Misidentifying these can delay proper stroke care.

Chameleon	Details
Acute Delirium	Left hemisphere strokes can cause confusion and dysphasia, mimicking delirium.
Cauda Equina Syndrome	Spinal cord infarction can present with bowel and bladder issues and lower limb weakness.
Monoparesis	Monoparesis due to focal ACA infarction may be mistaken for peripheral nerve injury or myelopathy.
Syncope	Loss of consciousness, especially with brief weakness, may be confused with a stroke.
Hypertensive Emergency	Elevated blood pressure in stroke may mimic a hypertensive crisis rather than a neurological event.
Acute Ataxia	Cerebellar strokes may appear as intoxication; symptoms like ataxia may lead to misdiagnosis.
Vestibular Neuronitis	Vertigo from lateral medullary or pontine strokes can be misinterpreted as vestibular neuronitis.

References and Further Reading

[1] Fernandes PM, Whiteley WN, Hart SR, et al. Strokes: mimics and chameleons. Practical Neurology 2013;13:21-28.

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