Modalities of Sensation to be Tested

Sensory examination broadly categorizes sensations into exteroceptive, proprioceptive, and cortical.

1. Exteroceptive (Superficial) Sensations

   • Pain (Superficial Pain)

     • Purpose: To assess the spinothalamic tracts.

     • Method: Use a sharp pin or a broken wooden tongue depressor, avoiding excessive pressure that might cause deep pain. Apply the stimulus intermittently and randomly to various parts of the body, comparing corresponding areas on both sides. Ask the patient if they feel the "prick" and if it feels the same on both sides. Discard the pin after use due to infection risk.

     • Abnormalities: Hypoalgesia (reduced pain sensation) or Analgesia (absent pain sensation).

   • Touch (Light Touch)

     • Purpose: To assess both anterior spinothalamic tracts and posterior columns.

     • Method: Use a wisp of cotton wool or a camel hair brush. Gently touch the skin, avoiding pressure. Ask the patient to say "yes" when they feel the touch. Compare symmetrical areas and test dermatomes.

     • Abnormalities: Hypoaesthesia (reduced touch sensation) or Anaesthesia (absent touch sensation).

   • Temperature

     • Purpose: To assess the lateral spinothalamic tracts.

     • Method: Use two test tubes, one with cold water (around 30°C) and one with warm water (around 44°C). Avoid extreme temperatures to prevent stimulating pain fibers. Apply the tubes randomly and ask the patient to identify "hot" or "cold" and compare sensations on both sides.

     • Abnormalities: Thermoanaesthesia (inability to distinguish hot/cold), Thermohypoaesthesia (reduced ability), or Thermohyperanaesthesia (exaggerated response).

2. Proprioceptive (Deep) Sensations

   • Joint Position Sense (Proprioception)

     • Purpose: To assess the posterior columns.

     • Method: Test the distal interphalangeal joint of the great toe and then fingers. Hold the digit by its sides, demonstrate "up" and "down" movements with the patient's eyes open. Then, with eyes closed, move the digit slightly and ask the patient to identify the direction of movement. Progress proximally to larger joints if distal sensation is impaired.

     • Abnormalities: Loss of position sense (proprioceptive loss).

   • Vibration Sense (Pallesthesia)

     • Purpose: To assess the posterior columns.

     • Method: Use a 128 Hz tuning fork. Strike the fork and place its base on bony prominences (e.g., great toe, ankle, shin, iliac spine, wrist, elbow, clavicle). Ask the patient to report when they feel the vibration and when it stops. Compare symmetrical areas.

     • Abnormalities: Pallhypoaesthesia (reduced vibration sensation) or Pallanaesthesia (absent vibration sensation).

   • Deep Pain

     • Method: Squeeze muscles (e.g., calf muscles) or tendons. This is a less commonly performed test.

3. Cortical Sensations

   • These sensations rely on the integration of primary sensory inputs by the cerebral cortex. Prerequisites include intact superficial and deep sensations.

   • Tactile Localization (Topognosis)

     • Method: Touch the patient's skin at various points with a cotton wisp or your fingertip. With eyes closed, ask the patient to point to where they were touched.

     • Abnormalities: Poor localization (atopognosis).

   • Two-Point Discrimination

     • Method: Use a two-point discriminator or calipers. Simultaneously touch the skin with two points and ask the patient if they feel one or two points. Gradually decrease the distance until only one point is perceived. Compare symmetrical areas. Normal distances vary by body region (e.g., 2-8 mm on fingertips, 40-75 mm on arms).

     • Abnormalities: Inability to discriminate two points at normal distances.

   • Stereognosis

     • Purpose: The ability to recognize an object by feel of its size and shape.

     • Method: With the patient's eyes closed, place familiar objects (e.g., coin, key, comb) in their hand and ask them to identify the object.

     • Abnormalities: Astereognosis (inability to identify objects by touch).

   • Graphaesthesia (Number Identification)

     • Purpose: The ability to "read" a number traced on the skin.

     • Method: With a blunt object (e.g., pen cap or fingertip), trace a number or letter on the patient's palm, asking them to identify it. Trace numbers large enough for clear perception.

     • Abnormalities: Agraphaesthesia (inability to identify traced numbers).

   • Extinction (Tactile Inattention)

     • Method: Simultaneously touch corresponding areas on both sides of the body. Ask the patient how many stimuli they feel. This can also be done with other sensory stimuli like pain.

     • Abnormalities: Sensation felt only on one side, indicating extinction on the contralateral side (often seen in non-dominant parietal lobe lesions)

   Note :Comparison: Always compare responses on both sides of the body. When mapping an area of sensory abnormality, proceed from the abnormal area to the normal area.