Anesthesia is defined as the absence of cutaneous sensation, including touch, temperature, and pain. It may be partial or total, and can affect one side of the body (unilateral) or both sides (bilateral). Anesthesia can result from neurological injury, peripheral nerve lesions, spinal cord pathology, or systemic conditions.

Pathophysiology

Normal sensation is transmitted via peripheral sensory nerves to the spinal cord and then to the brain’s somatosensory cortex. Lesions or damage at any point along this pathway—whether due to trauma, ischemia, demyelination, infection, or compression—can interrupt sensory transmission, resulting in anesthesia. Examples include:

• Peripheral nerve injury: Trauma or compression causing localized anesthesia.

• Spinal cord lesions: Hemisection (Brown-Séquard syndrome) or transverse myelitis causing dermatomal sensory loss.

• Cortical lesions: Stroke affecting the postcentral gyrus producing contralateral sensory deficits.

• Metabolic or systemic conditions: Diabetes mellitus or chronic vitamin deficiencies leading to peripheral neuropathy.

Examination technique

1. Patient positioning: Ensure the patient is comfortably seated or lying down.

2. Instruction: Ask the patient to close the eyes to prevent visual cues.

3. Testing: Lightly touch the skin with a cotton wisp, blunt object, or temperature probe.

4. Assessment: Ask the patient to identify the location and type of stimulus (touch, temperature, or pain).

5. Observation: For patients with immature or limited verbal skills, watch for reflexive movements, flinching, or facial expressions in response to stimuli.

6. Documentation: Map the areas of sensory loss and note whether they are unilateral, bilateral, partial, or complete.

Clinical utility

• Diagnostic tool: Helps localize neurological lesions in peripheral nerves, spinal cord, or brain.

• Monitoring progression: Useful in tracking neuropathy, nerve recovery, or effects of spinal anesthesia.

• Surgical and anesthetic planning: Preoperative sensory assessment guides regional or local anesthesia strategies.

Differential diagnosis

Pediatric considerations

• Children may have difficulty describing sensory loss.

• Observation of withdrawal or facial expression is essential.

• Be gentle to avoid fear or false negatives.

Geriatric considerations

• Older adults may have subtle or slowly progressive sensory deficits due to peripheral neuropathy or stroke.

• Sensory mapping may help prevent injuries and assess fall risk.

Limitations

• Patient cooperation is essential for accurate localization.

• Subtle deficits may require electrophysiological studies or imaging.

• Cannot reliably differentiate central vs. peripheral lesions without adjunctive testing.

Patient counseling

• Explain the purpose of sensory testing and expected responses.

• Advise the patient on protecting areas with sensory loss to prevent burns, cuts, or trauma.

• Discuss follow-up evaluation if progressive sensory loss is noted.

Conclusion

Anesthesia is a key neurological sign that provides important information about the integrity of sensory pathways. Proper assessment allows clinicians to localize lesions, monitor progression, and guide management. Interpretation should always consider history, neurological examination, and supportive investigations.

References

1. Buttaro TM, Tybulski J, Bailey PP, Sandberg-Cook J. Primary Care: A Collaborative Practice. St. Louis, MO: Mosby Elsevier; 2008:444–447.

2. McCance KL, Huether SE, Brashers VL, Rote NS. Pathophysiology: The Biologic Basis for Disease in Adults and Children. 7th ed. Maryland Heights, MO: Mosby Elsevier; 2010.

3. Colyar MR. Well-Child Assessment for Primary Care Providers. Philadelphia, PA: F.A. Davis; 2003.

4. Tintinalli JE, Stapczynski JS, Ma OJ, Yealy DM. Tintinalli’s Emergency Medicine: A Comprehensive Study Guide. 9th ed. New York, NY: McGraw-Hill; 2020.