Sensation Testing Guide: Light Touch & Sharp/Dull Exam

Sensory examination tests ascending pathways: spinothalamic tracts (pain/temperature) and dorsal columns (vibration/proprioception). Pain is tested with sterile pin after explaining sensation. Temperature uses cold/warm tubes. Proprioception tests joint position sense by moving joints and identifying direction. Vibration uses 128 Hz tuning fork, starting distally and progressing proximally. Key dermatome landmarks: C8 (middle finger), T5 (nipple), T10 (umbilicus), T12 (inguinal ligament). Abnormal proprioception requires testing proximal joints. Comparison between limbs is essential.

Sensory examination evaluates four modalities: pain (sharp objects like toothpick), temperature (cold preferred over hot), vibration (tuning fork 128 Hz placed on bone), and proprioception (joint position sense). Control testing establishes baseline sensation before examining limbs. Testing proceeds distally to proximally with eyes closed. Normal sensation shows consistent response throughout. Pathological patterns typically show distal impairment progressing proximally. Vibration testing compares patient's threshold to examiner's threshold. Proprioception testing holds the finger from the sides and moves it up and down while the patient identifies direction changes.

The sensory exam evaluates four modalities through the spinothalamic and dorsal column-medial lemniscus pathways. Pain and temperature are tested using sharp objects like broken cotton swabs, starting distally and comparing left-to-right. Vibration uses a 128Hz or 256Hz tuning fork on bones, moving to different locations to assess distribution. Proprioception isolates the distal interphalangeal joint and moves it up/down while the patient identifies direction without visual cues. Testing is subjective and relies on patient honesty. Both vibration and proprioception can be tested interchangeably since they share the same pathway.

A comprehensive upper limb neurological examination assesses six sensory modalities: light touch (using neuroilament), fine touch (cotton wool), sharp-dull discrimination (sharpened point), vibration (tuning fork), proprioception (thumb positioning), and temperature (cold/warm stimuli), with normal findings indicating intact sensory function across all dermatomes.

To test sensory function systematically: First test that the patient can feel the stimulus and understands what to do by testing on a part where sensation is known to be normal. If sensory loss appears glove or stocking distributed, start at the tips of fingers or toes and work upward until finding the sensory level. Test vibration sense using a C128 tuning fork on upper and lower limbs and trunk. Test proprioception (joint position sense) with eyes closed: separate the digit from adjacent digits, move the joint up and/or down, and ask the patient which direction the digit is being moved. Temperature testing is difficult in normal clinical settings but should be performed if abnormality is suspected.

Cortical sensory function is assessed through stereognosis (object recognition by touch with eyes closed), two-point discrimination (minimum distance to differentiate touch points, 3mm on fingertips), and graphesthesia (recognizing written numbers on palm with eyes closed); these tests depend on intact dorsal column-medial lemniscal pathway (first-order neurons in dorsal root ganglia → posterior columns → medulla nuclei → thalamus → sensory cortex), and lesions in the somatosensory cortex or thalamus (ventral posterior lateral/medial nuclei) cause contralateral deficits in discriminative touch, localization, proprioception, and stereognosis, with thalamic lesions potentially causing Dejerine-Roussy syndrome (severe post-stroke pain).

Cortical sensory function is assessed by testing the parietal lobe and association areas. The graphesthesia test involves the patient closing their eyes while the examiner writes numbers on their palm, and the patient identifies the number. The stereognosis test involves the patient identifying objects placed in their hand while their eyes are closed. These tests assess higher-order sensory processing.

Cortical sensory functions require intact parietal lobe function. Stereognosis assesses object recognition by touch, asking patients to describe objects' shape, consistency, and material with eyes closed. Graphaesthesia evaluates recognition of symbols, letters, or numbers drawn on the skin with a blunt scalpel, demonstrated first with eyes open then tested with eyes closed. Two-point discrimination tests the ability to distinguish simultaneous tactile stimuli using a compass with adjustable points, with point distance varying by body area (smaller for fingertips, larger for other areas). These tests assess higher-order sensory processing and cortical integration.

Cortical sensory examination performed only after superficial and deep pathways confirmed intact: (1) Two-point discrimination tests ability to distinguish two separate points, (2) Stereognosis tests ability to recognize familiar objects by touch, (3) Graphesthesia tests ability to recognize numbers/letters written on palm. These tests assess somatosensory cortex integrity. Normal thresholds vary by body location.

Cortical sensation tests include tactile localization, two-point discrimination, stereognosis, and agraphesthesia. Before performing these tests, normal spinotheralamic sensation (touch, pain, temperature, position, vibration) must be confirmed. Tactile localization is tested by placing an object on the patient's body while their eyes are closed and asking them to identify the exact location. Two-point discrimination is tested by placing two points on the patient's body while their eyes are closed and asking if they feel one or two points. Normal values are: 5mm for finger tips (most sensitive), 4cm for dorsum of foot (less sensitive), and 5-7cm for trunk (least sensitive). Stereognosis is tested by placing familiar objects in the patient's hand while their eyes are closed and asking them to identify the object. Agraphia is tested by writing letters and numbers on the patient's forearm and palm while their eyes are closed and asking them to identify what was written.

The complete neurological examination integrates motor, sensory, and reflex testing within a systematic framework. Motor assessment evaluates muscle groups through resistance testing (finger abduction, fist making, shoulder shrugging, knee extension, straight leg raising) with appropriate force application—using full body weight for lower extremities while avoiding injury. Sensory testing examines two major pathways: posterior column-medial lemniscus (vibration, proprioception, fine touch) and spinothalamic tract (pain, temperature), with vibration testing being more sensitive and quicker. Reflex testing includes knee clonus (placing fingers above kneecap and wiggling while pushing down to observe rhythmic contraction-relaxation cycles). The brain organizes motor neurons in a U-shaped arrangement along the motor strip, representing functional movements rather than individual muscles. Proper technique requires pushing against the patient's own muscle group rather than using body weight or opposite limbs, with sensitivity taking precedence over specificity to detect early signs of conditions like transverse myelitis.

This video demonstrates the complete neurological examination, covering motor assessment (inspection for muscle bulk and abnormal movements, pronator drift test for corticospinal lesions, tone assessment for rigidity/spasticity/flaccidity, and MRC power grading from 0-5), reflex testing using the deep tendon reflex scale (0-4) with weighted/unweighted hammers, and sensory evaluation of five modalities (temperature, pain, touch, vibration, proprioception) to assess the spinothalamic and posterior column-medial lemniscus tracts, with sensory deficits presenting in dermatomal or peripheral nerve patterns depending on lesion location.

Systematic neurological examination includes: cranial nerves (vision, hearing, facial function, swallowing); motor system (muscle bulk, tone, power, reflexes); sensory system (pain, temperature, vibration, proprioception, cortical sensations); cerebellar function (finger-nose, heel-shin, Romberg's); and higher mental functions. Reflex levels (trapezius C2-C4, biceps C5-C6, knee C3-C4) help localize lesions. Hyperreflexia with clonus indicates upper motor neuron involvement. Sensory level helps localize the lesion.

The neurological examination follows a systematic framework: (1) Higher mental functions, (2) Cranial nerves 1-12, (3) Motor system (bulk, tone, power, reflexes, coordination), (4) Sensory system, (5) Gait assessment. Motor examination includes inspection for wasting/hypertrophy, tone assessment (spasticity from corticospinal lesions, rigidity from extrapyramidal lesions), power grading (0-5 scale), and reflex testing (deep tendon: supinator, biceps, triceps, knee jerk, ankle jerk; superficial: abdominal, cremaster, plantar). Babinski's reflex indicates corticospinal tract lesion. Coordination tests cerebellar function (finger-to-nose, dysdiadochokinesia, knee-heel test). Sensory examination tests spinothalamic tracts (pain/temperature) and dorsal columns (vibration/proprioception). Cortical sensations include two-point discrimination, stereognosis, graphaesthesia. Gait assessment identifies patterns: festive (Parkinson's), circumduction (peripheral nerve), cerebellar (broad-based). Romberg's test distinguishes sensory ataxia from cerebral lesions.

A comprehensive neurological examination systematically assesses motor function (muscle strength, tone, reflexes), sensory function (light touch, sharp/dull sensation, joint position sense), cerebellar coordination (finger-to-nose, heel-to-shin, rapid alternating movements), and gait/balance (Romberg test, heel-to-toe walking). The exam includes cranial nerve testing, deep tendon reflexes (biceps, triceps, brachioradialis, patellar, Achilles), and meningeal signs (Kernig's, Brudzinski's, nuchal rigidity) to evaluate neurological function and identify potential pathology.

Test light touch first with cotton buds (not hands, which test thermal sensation), then pinprick for small fiber assessment. Compare affected to unaffected side or use abdomen/thigh for bilateral comparison. Test in loops around limbs (upper leg, lower leg, tops of toes) rather than strict dermatomes. In radiculopathy, sensory loss is typically fuzzy with overlapping nerve root function; in peripheral neuropathy, loss is clearly delineated. Pinprick often reveals additional sensory deficits not detected by light touch alone.

Objectifying sensory exams involves having patients point to where they feel sensations and describe what they feel. For peripheral neuropathies, vibration testing uses tuning forks on bony prominences, with clinicians moving up the leg if ankle sensation is absent. Two-point discrimination tests tactile acuity using calipers. Diabetic foot sensation testing evaluates L4, L5, and S1 dermatomes on the lateral foot using a disposable pin. A positive test indicates loss of protective sensation. Clinical considerations include testing in quiet rooms, performing multiple trials per area (50/50 guessing chance), and recognizing that cortical lesions (neglect) may cause non-detection even with intact sensory tracts.

This segment covers sensory examination in peripheral neuropathy. Sensory examination includes light touch, pain and temperature, vibration sense, joint position sense, and cortical sensation (two-point discrimination, tactile localization, stereognosis, graphesthesia). The examination should be performed systematically and note any asymmetry. The patient had impaired pain, touch, and temperature below knee and absent below ankles, impaired vibration sense below knee and absent at knee joint and ankle. These findings indicate large fiber involvement. The sensory loss pattern (below knee and ankle) indicates involvement of sensory tracts at the level of the peripheral nerves or spinal cord.

Sensory examination in peripheral neuropathy includes testing subjective symptoms (paresthesias, burning, pain) and objective deficits. Deep sensation (proprioception) is tested using a tuning fork placed on bony surfaces. Position sense is tested by moving toes/fingers with eyes closed. Temperature and pain sensation are tested using warm and cold objects. Diabetic neuropathy typically presents with 'glove and stocking' sensory loss, affecting feet and hands symmetrically.

Sensory testing follows a dermatomal pattern validated against the sternum. For pin prick and light touch, the examiner tests L1 through S1 dermatomes systematically. If peripheral neuropathy is suspected, testing begins distally at toe tips and progresses proximally. Normal sensation is confirmed when the patient can feel sharpness or touch at all tested sites. The pattern helps localize spinal cord or peripheral nerve pathology.