Focal Neurological Deficits
Focal neurological deficits are new or worsened neurological symptoms or signs that are anatomically referable to a specific brain region, indicating localized dysfunction of the central nervous system. 1
Definition and Classification
Focal neurological deficits (FNDs) are characterized by:
- Symptoms and signs that can be attributed to a particular brain region or pathway 2
- May be transient or persistent, depending on the underlying cause and duration 1
- Can manifest as motor weakness, sensory disturbances, visual field defects, language impairment, or other localized neurological dysfunction 1
FNDs can be classified based on their relationship to hemorrhage:
- Hemorrhagic FND: Associated with radiological, pathological, surgical, or cerebrospinal fluid evidence of recent bleeding 1
- Non-hemorrhagic FND (NH-FND): Neurological deficits without evidence of recent bleeding on imaging or examination 1
- FND not otherwise specified (NOS-FND): When appropriate investigations haven't been performed to determine if hemorrhage is present 1
Duration-Based Classification
FNDs can be further categorized by duration:
- Transient FND: Resolves within 24 hours 1
- Persistent FND: Lasts more than 24 hours and remains static or improves 1
- Progressive FND: Lasts more than 24 hours with continued deterioration 1
Common Causes
Focal neurological deficits can result from various pathologies:
- Stroke (ischemic or hemorrhagic): Sudden onset of focal deficits due to interruption of blood supply or bleeding 1, 3
- Intracranial hemorrhage: Including intracerebral, subarachnoid, subdural, or epidural hemorrhage 4
- Brain tumors: May cause progressive focal deficits through direct compression or surrounding edema 5, 6
- Cavernous malformations (CM): Can cause FNDs through hemorrhage, mass effect, or edema 1
- Traumatic brain injury: Focal damage to specific brain regions 1
- Seizures: Post-ictal Todd's paralysis can cause temporary focal weakness 1, 4
- Infectious processes: Brain abscesses or encephalitis can cause focal deficits, especially in febrile contexts 2
- Migraine: Can present with transient focal neurological symptoms 1, 3
Clinical Evaluation
When evaluating a patient with focal neurological deficits:
- Determine the anatomical localization based on the specific deficits 1, 3
- Assess for acute onset versus gradual progression 3
- Document the duration and evolution of symptoms 1
- Use standardized neurological examination tools like the NIH Stroke Scale (NIHSS) to quantify deficits 1
- Consider the patient's medical history, particularly vascular risk factors or prior neurological events 1
Diagnostic Approach
Appropriate investigations for focal neurological deficits include:
- Brain imaging: CT or MRI should be performed as soon as possible after symptom onset 1
- Cerebrospinal fluid examination: May show evidence of hemorrhage or infection in selected cases 1
- EEG: Particularly valuable for focal deficits in febrile contexts or when seizures are suspected 2
Impact on Brain Function
Focal brain lesions can have widespread effects:
- Damage to connector regions (areas important for communication between brain networks) can disrupt overall brain network organization 5
- Effects can extend beyond the anatomical location of the lesion, affecting the structurally intact hemisphere 5
- Sedatives can unmask or exacerbate underlying focal deficits, particularly in patients with prior motor dysfunction 6
Outcome Assessment
For standardized assessment of patients with focal neurological deficits:
- NIH Stroke Scale (NIHSS) for measuring neurological impairment 1
- Modified Rankin Scale (mRS) for measuring disability and handicap 1
- Health-related quality of life measures such as SF-36 or EQ-5D 1
- Follow-up assessments at 1,6, and 12 months after onset for monitoring recovery 1
Clinical Significance
Focal neurological deficits are important clinical findings that: