What are the common causes of transient neurologic deficits when CT and MRI imaging are normal?

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Common Causes of Transient Neurologic Deficits with Negative Imaging

Primary Differential Diagnosis

The most common causes of transient neurologic deficits with normal CT and MRI include transient ischemic attacks (TIAs), migraine aura without headache, focal seizures, and in elderly patients with microbleeds, transient focal neurological episodes related to cerebral amyloid angiopathy.

Transient Ischemic Attack (TIA)

  • TIA remains the most critical diagnosis to consider despite negative imaging, as MRI shows acute ischemic lesions in only 31% of TIA patients, meaning approximately two-thirds have no visible brain lesion even with MRI and contrast. 1
  • More recent data confirms that MRI evidence of acute ischemia appears in only 42% of patients meeting National Institute of Neurological Disorders and Stroke criteria for TIA/stroke, leaving 58% with negative imaging. 2
  • Patients with TIA and negative MRI still carry significant stroke risk: those with MRI evidence of acute ischemia have an 18% stroke rate by 18 months versus 1% without MRI lesions (age-adjusted hazard ratio 13). 2
  • Clinical features favoring TIA include: older age (mean 65 years), male predominance, inaugural episode (94% of cases), history of stroke, hypertension, and dyslipidemia. 3
  • Visual deficits occur in only 10% of TIA patients, compared to higher rates in migraine aura. 3

Migraine Aura Without Headache (MAWH)

  • MAWH is a major TIA mimic that cannot be reliably distinguished from TIA using current validated criteria, leading to diagnostic confusion in clinical practice. 3
  • Patients with MAWH are typically younger (mean age 50 years) and predominantly female. 3
  • Visual deficits occur in 63% of MAWH cases, significantly higher than TIA. 3
  • The key distinguishing feature is that MAWH is rarely inaugural (only 19% of cases), whereas TIA is inaugural in 94% of cases. 3
  • MRI evidence of acute ischemia can still appear in 11% of patients with migraine aura, complicating the diagnostic picture. 2

Focal Seizures

  • Focal seizures present with transient neurologic deficits and typically normal structural imaging in the acute setting. 4
  • Patients with seizures may have normal MRI on 1.5T scanners but show abnormalities on 3.0T scanners, even with unchanged seizure semiology. 4
  • EEG may show focal slowing as the first evidence of underlying pathology before imaging becomes positive. 5

Cerebral Amyloid Angiopathy (CAA)-Related Episodes

  • In elderly patients, transient focal neurological episodes may be related to CAA with superficial cortical siderosis or focal convexity subarachnoid hemorrhage, mimicking TIA but actually representing bleeding rather than ischemia. 6
  • These episodes herald a very high future risk of symptomatic intracerebral hemorrhage, making antiplatelet or anticoagulant therapy potentially dangerous. 6
  • Blood-sensitive MRI sequences (gradient-echo, susceptibility-weighted imaging) are essential for detecting microbleeds and cortical siderosis. 6

Occult Brain Tumors

  • Malignant astrocytomas can present with transient neurologic disturbances (mimicking seizures or TIAs) with completely normal CT scans initially, only becoming visible 4.5 months later. 5
  • EEG may show focal slowing before CT becomes positive. 5
  • This represents 4% of malignant astrocytomas in one series. 5

Diagnostic Algorithm

Initial Clinical Assessment

  • Age >65 years, male sex, vascular risk factors (hypertension, dyslipidemia, prior stroke), and inaugural episode strongly favor TIA over migraine aura. 3
  • Visual symptoms in 63% of cases with recurrent episodes favor MAWH over TIA. 3
  • Obtain detailed history of prior similar episodes—recurrent stereotyped events favor migraine or seizures over TIA. 3

Imaging Strategy

  • MRI with diffusion-weighted imaging should be performed within 5 days of symptom onset, as it detects acute ischemia in 31-42% of TIA patients. 1, 2
  • Include blood-sensitive sequences (T2 gradient-echo or susceptibility-weighted imaging) to detect microbleeds and cortical siderosis suggesting CAA.* 6
  • Contrast enhancement contributes to acute lesion delineation in only 4% of TIA patients and is generally not necessary. 1
  • If initial MRI is negative but clinical suspicion for tumor remains (especially with focal EEG slowing), repeat MRI in 3-6 months. 5

Risk Stratification After Negative Imaging

  • Even with negative MRI, patients with probable TIA diagnosis require full vascular workup and secondary stroke prevention, as they still carry stroke risk. 1, 2
  • The presence of identifiable vascular or cardiac causes is significantly higher in TIA patients with MRI-visible infarction (odds ratio 5.2), but absence of lesions does not exclude significant vascular disease. 1
  • In patients with microbleeds or cortical siderosis on blood-sensitive sequences, avoid antiplatelet or anticoagulant therapy due to high intracerebral hemorrhage risk. 6

Critical Pitfalls to Avoid

  • Do not assume negative imaging excludes TIA—two-thirds of TIA patients have no visible lesion on MRI. 1
  • Do not use standard MRI sequences alone in elderly patients—blood-sensitive sequences are essential to detect CAA-related episodes that contraindicate antithrombotic therapy. 6
  • Do not dismiss recurrent stereotyped episodes as "just migraine" without considering focal seizures or CAA, especially in older patients. 3, 6
  • Do not stop diagnostic workup after one negative CT/MRI if clinical suspicion remains high—tumors can become visible months later. 5
  • Recognize that there is no single clinical or paraclinical feature that accurately distinguishes TIA from migraine aura when using validated criteria, requiring comprehensive evaluation. 3

References

3
Research

Transient Neurologic Deficits: Can Transient Ischemic Attacks Be Discriminated from Migraine Aura without Headache?

Journal of stroke and cerebrovascular diseases : the official journal of National Stroke Association, 2015

4
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

6
Research

Transient focal neurological episodes, cerebral amyloid angiopathy, and intracerebral hemorrhage risk: looking beyond TIAs.

International journal of stroke : official journal of the International Stroke Society, 2013

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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