To check sensory level, you perform a detailed examination of specific areas on the body known as dermatomes to identify the lowest point where sensation is normal.
The sensory level is determined by performing an examination of the key sensory points within each of the 28 dermatomes on each side of the body (right and left). It is defined as the most caudal, normally innervated dermatome for both pin prick (sharp/dull discrimination) and light touch sensation.
Understanding the Sensory Examination Process
Checking the sensory level is a crucial part of a neurological examination, often performed to assess spinal cord function after an injury or in neurological conditions. The process involves systematically testing sensation in specific areas of the skin that correspond to individual spinal nerves.
Key steps typically include:
- Identify the Dermatomes: The body is mapped into 28 key dermatomes on each side (C2-C4, C5-T1, T2-L1, L2-S1, S2-S4/5). Each dermatome represents an area of skin primarily supplied by a single spinal nerve root.
- Test Key Sensory Points: Within each dermatome, there are designated "key points" that are tested.
- Assess Modalities: Sensation is typically tested using at least two modalities:
- Pin Prick: Evaluates the ability to distinguish between sharp and dull stimuli, assessing the spinothalamic tract.
- Light Touch: Evaluates the ability to perceive light contact, assessing the dorsal column pathway.
- Systematic Testing: The examination proceeds systematically, usually moving from caudal (lower) to rostral (higher) dermatomes, or vice versa, on both sides of the body.
- Documentation: For each dermatome tested on both the left and right sides, the sensation for both pin prick and light touch is graded (e.g., normal, impaired, absent).
Determining the Sensory Level
Based on the examination, the sensory level is pinpointed:
- It is the most caudal (lowest) dermatome where both pin prick and light touch sensations are found to be normal on both sides of the body.
- If sensation is impaired or absent below this point, the sensory level indicates the approximate level of spinal cord involvement affecting sensation.
Practical Examination Steps
Here's a simplified overview of the practical steps involved in checking the sensory level:
- Preparation: Ensure the patient is comfortable and understands the procedure. Use appropriate tools (e.g., a safety pin or neurotip for pin prick, a wisp of cotton or soft brush for light touch).
- Demonstration: Show the patient what the pin prick (sharp vs. dull) and light touch sensations feel like on an area they know has normal sensation (e.g., their cheek).
- Test Systematically: Begin testing each key sensory point within each dermatome, moving consistently from lower to higher levels or vice versa. Compare findings on the left and right sides.
- Record Findings: Document the sensation (normal, impaired, absent) for both pin prick and light touch in each dermatome on both sides.
- Identify the Level: The lowest dermatome where both pin prick and light touch are recorded as normal on both sides is the sensory level.
| Modality | Dermatome Level | Right Side | Left Side |
|---|---|---|---|
| Pin Prick | S1 | Impaired | Impaired |
| L5 | Normal | Normal | |
| L4 | Normal | Normal | |
| Light Touch | S1 | Absent | Absent |
| L5 | Normal | Normal | |
| L4 | Normal | Normal |
In this example, the sensory level for both pin prick and light touch would be L5, as this is the most caudal dermatome where both sensations were found to be normal bilaterally.
Checking the sensory level provides vital information about the extent of sensory pathway function and helps localize potential issues within the spinal cord.
