Understanding Somatosensation

• Somatosensation refers to the sensation received from the integumentary and musculoskeletal systems
• This differs from specialized senses like sight and hearing

Why Somatosensation Matters

• Understanding the competence/integrity of the nervous system is key
• Function provides a basis for PT patient/client management
• Assessing the extent of sensory loss is important to understand the nervous system
• Assessment primarily focuses on nerve roots and peripheral nerves
• It also gathers information on spinal tracts and brain function.
• Somatosensation assists in diagnosis, provides prognostic information, and direction for intervention
• It aids in evaluating and documenting sensory recovery.
• Sensation plays a role in movement, guiding motor responses based on environmental context.
• It helps adapt movements and shape motor programs through feedback for corrective action
• Sensation enables feedback, feedforward, and protection mechanisms.

When to Examine Somatosensation

• Clinical indications such as risk factors, health/wellness needs, and pathology/health conditions necessitate examination
• Examine somatosensation if there are impairments and activity limitations
• Information can be gathered from patient history by noting primary concerns, associated symptoms, systems review, medical history, and functional limitations
• Systems review can also provide information through observation, strength screen, reflexes, and dermatomal screens.

Examples of Sensory Dysfunction

• Peripheral nerve damage (trauma, impingement/compression)
• Metabolic issues (diabetes, thyroid issues)
• Spinal cord injury
• Burns
• Toxins (chemotherapy, mercury, lead)
• Brain diseases (MS, ALS)
• Infections (Lyme disease, shingles, HIV)
• Sensory dysfunction leads to imbalance, difficulty gripping objects, and repeated injuries.

Anatomy and Sources of Dysfunction

• Includes sensory receptors, peripheral nerves, nerve roots, spinal cord, and brain

Sensory Receptors

• Mechanoreceptors respond to mechanical deformation
• Thermoreceptors respond to temperature
• Nociceptors respond to pain
• Chemoreceptors respond to chemical substances
• Photoreceptors respond to visible light

Sensory Receptor Levels

• Superficial sensation comes from exteroceptors receiving info from external sources, like pain, temp, and light touch pressure
• Deep sensation comes from proprioceptors and receive info from muscles, tendons, ligaments, joints and fascia
• Position sense, joint resting position, movement, and vibration fall under this
• Combined cortical sensations require info from both
• Some examples are stereognosis, 2-point discrimination, barognosis, graphesthesia, tactile localization, texture, and double simultaneous stimulation

Organization of Nerves

• Includes spinal cord, nerve roots, spinal nerves, plexus, and peripheral nerves

Anatomy: Spinal Nerve Dermatomes

• Spinal nerve dermatomes are areas of skin innervated by specific spinal nerve roots

Anatomy: Tracts

• The dorsal column system carries fine, discriminative touch and pressure, proprioception, and vibration
• The spinothalamic tract carries pain and temperature, as well as crude, non-discriminative touch and pressure

Somatosensory Cortex Function

• Areas with high sensitivity have more representation
• Functions by processing movement
• It determines initial position before movement, detects errors as movement occurs, and identifies movement outcomes through learning

Sources of Sensory Dysfunction

• Central nervous system (CNS): brain, nuclei, spinal cord, tracts can have a stroke, multiple sclerosis, or a spinal cord lesion
• Peripheral nervous system (PNS): spinal nerves, peripheral nerves, sensory receptors can have compression/cut/crush injuries, radiculopathy/neuropathy, or burns

Types of Nerve Injuries

• Myelopathy: affects the spinal cord
• Nerve Root Avulsion: nerve root is torn away from the spinal cord
• Radiculopathy: affects nerve roots
• Plexopathy: injury to a nerve plexus
• Neuropathy: general term for nerve damage
• Mononeuropathy: affects a single nerve
• Polyneuropathy: affects multiple nerves
• Double Crush: multiple sites of compression along a nerve
• Neural Tension: abnormal stress on a nerve

Peripheral Nerve Injuries

• May include compression, blunt trauma, stretch, avulsion, severing, and disease.

Wallerian Degeneration

• The degeneration of myelin and axons distal to the site of nerve injury

Seddon's Classification for Nerve Injuries

• Neuropraxia is a transient physiologic block caused by ischemia/pressure with no Wallerian degeneration
• Axonotmesis has preserved architecture, but axons are damaged with Wallerian degeneration; recovery takes months
• Neurotmesis: nerve structure is destroyed, requiring surgery; recovery is limited

Examination: How We Do It

• Includes history, systems review, and tests and measures, perform formal somatosensory testing

Subjective Information

• Consider neurological issues by exploring any numbness, tingling, or changes in sensation

Objective- Systems Review

• Impairment on a light touch screen may suggest a need for formal somatosensory testing

Which Somatosensory Test

• Depends on overall goal
• Some tests that can be performed include -Touch awareness (x2)
  • Pain perception
  • Temperature
  • Kinesthesia awareness
  • Proprioception awareness
  • Vibration perception
  • Stereognosis
  • Tactile localization
  • Two-point discrimination
  • Double simultaneous stimulation
  • Graphestesia
  • Texture recognition
  • Barognosis

Process: Therapist Preparation

• Knowledge of anatomy and identifying neurological patterns are needed before examination
• Rehearse reps to improve consistency in pressure and delivery
• Have equipment, tools (if needed), marking pencil (if needed), documentation paper/chart, and something to occlude vision

Tools for Touch Awareness

• Camel hair brush
• Cotton swab or ball
• Tissue
• Monofilaments

Tools: Monofilaments

• Apply perpendicular to skin and press until bent, hold for 1-2 seconds
• A gauge of > 5.07/10g indicates loss of protective sensation on the plantar surface of foot
• Gauge ≤ 2.83/.07g = normal sensation throughout most of the body

Pressure/Monofilament Testing Norms

• Apply perpendicular to skin
• Apply the monofilament for for 1-2 seconds

Process: Patient Preparation

• Give a full explanation of the test and purpose
• Ensure patient is cognitively able, alert and oriented, and able to concentrate/focus
• Ensure patient can tolerate testing
• Demonstrate the test, ensure vision is enabled, and orient patient to what to expect
• Avoid the patient guessing to improve validity and reliability in responses
• Instruct patient NOT to guess

Process: Carrying out the Exam

• Eliminate vision
• Strategies include organized/predictable vs disorganized variable/unpredictable vs controlled variable/unpredictable
• Consider location, cadence, and timing (at least 2 seconds in between)
• Begin with a broad screen then become more specific
• Be aware of patient fatigue
• Bilaterally, distal to proximal or circumfrentially
• Perform multiple trials for verification (x3)
• Map exact boundaries using a skin marker or image/chart

How to Apply Previous Steps to Other Tests

• Pain: Use a similar process with sharp/dull variables.
• Localization: Use a similar process, adding instructions to indicate where.
• Pressure: maintain consistent pressure.
• Double Simultaneous Stimulation: Apply two points at once without detailed mapping.

Evaluation

• Need to assess for sensation patterns and cross reference with any myotomes, motor nerve innervation, or sclerotomes

Evaluation: The What? Common Patterns of Sensory Loss

• CVA: Loss depends on the location of the infarct.
• MS: Loss tends to be unpredictable and scattered.
• Peripheral Neuropathy (e.g., Diabetes): Presents as a stocking and glove pattern.
• Spinal Cord Injury: Diffuse loss below the level of the injury.
• Spinal Nerve Root: Loss follows a dermatomal pattern with lots of overlap.
• Peripheral Nerve: Loss will present with in a specific cutaneous sensory distribution

Evaluation: Reporting the Results

• Include the sensation tested, tool used, body surface affected (with map)
• Document the outcome (intact, absent, impaired with description of level of intensity)
• Always take down the patients subjective responses as well as the impact this has on their function

Intervention

• Sensory integration focuses on enhancing sensory intake and recovery, using intrinsic and augmented feedback
• Compensatory approaches help manage symptoms and increase level of safety

Additional Considerations

• Examine the unaffected side for comparison
• Neural lesions may need time to develop after injury
• Be aware of double crush possibilities and neural tension in the patient
• Assess for sensory and motor loss, this could indicate neural or soft neural tissue lesion