What is a neurological focal deficit?

Neurological Focal Deficit

A neurological focal deficit is characterized by symptoms and signs that can be attributed to a specific brain region or neurological pathway, manifesting as motor weakness, sensory disturbances, visual field defects, language impairment, or other localized neurological dysfunction. 1

Definition and Classification

• Focal neurological deficits are clinical manifestations that can be anatomically localized to a particular area of the brain or specific neural pathway, and may be transient or persistent depending on the underlying cause 1

• These deficits represent dysfunction in a specific neuroanatomical location, as opposed to global or diffuse neurological dysfunction 1

• Focal deficits can be classified based on their relationship to hemorrhage 1:

  • Hemorrhagic focal neurological deficit
  • Non-hemorrhagic focal neurological deficit
  • Focal neurological deficit not otherwise specified (NOS-FND)

Duration-Based Classification

• Focal neurological deficits can be further categorized by their duration 2, 1:
  • Transient FND: Deficits that resolve within 24 hours
  • Persistent FND: Deficits that last 24 hours or longer and remain static or improve
  • Progressive FND: Deficits that last 24 hours or longer and continue to worsen

Clinical Manifestations

• Motor deficits: Weakness or paralysis affecting specific muscle groups (hemiparesis, monoparesis) 1

• Sensory disturbances: Numbness, tingling, or altered sensation in specific body regions 1

• Language impairments: Aphasia, dysarthria, or other speech/language disorders 1

• Visual field defects: Hemianopia, quadrantanopia, or other visual field losses 1

• Other localized neurological dysfunctions that can be attributed to specific brain regions 1

Common Causes

• Stroke (ischemic or hemorrhagic): Sudden onset of focal deficits due to interruption of blood supply or bleeding 1

• Cavernous malformations: Can cause focal deficits through hemorrhage, mass effect, or edema 2, 1

• Traumatic brain injury: Can cause focal damage to specific brain regions 1

• Seizures: Post-ictal Todd's paralysis can cause temporary focal weakness 1, 3

• Non-convulsive status epilepticus: Can present with focal deficits without obvious seizure activity 3

• Subarachnoid hemorrhage: Approximately 10% of aneurysmal SAH patients present with focal deficits 4

Diagnostic Approach

• Brain imaging should be performed as soon as possible after symptom onset 2, 1:

  • CT scan ideally within 1 week to demonstrate high density consistent with recent hemorrhage
  • MRI with appropriate sequences (GRE, FLAIR) to identify acute and subacute hemorrhage

• Cerebrospinal fluid examination may show evidence of hemorrhage in cases where a cavernous malformation is located near a pial surface 2

• EEG may be indicated in cases of suspected seizure activity or non-convulsive status epilepticus, particularly in febrile contexts 5, 3

Clinical Pitfalls and Considerations

• Dizziness as an isolated symptom does not meet the criteria for specific localization and is not considered a neurological focality 6

• However, acute persistent vertigo can be caused by posterior circulation stroke affecting the brainstem or cerebellum, and focal neurological signs may be absent in one-third to two-thirds of these patients 6

• The presence of focal neurological deficits at presentation of subarachnoid hemorrhage is independently associated with poor outcome 4

• The mere existence of a hemosiderin halo or solely an increase in cavernous malformation diameter without other evidence of recent hemorrhage is not considered to constitute hemorrhage 2