Dermatomes Lower Limb | Peripheral Neurological Examination

Dermatome assessment is an essential part of neurological examination when suspecting radiculopathy, as changes in sensation within a specific dermatome may help you identify the pathological disc level. Al Nazari et al. (2013) performed a systematic review and meta-analysis of 14 different studies investigating sensory, motor and reflex testing for lumbar disc herniations. The results showed that sensory testing had a sensitivity of 32-40% and a specificity of 59-72% which translated to a sensitivity of 35 and a specificity of 64 percent in the identification of the pathological disk level. Pooled positive likelihood ratios for all neurological examination components range between 1.02 and 1.26. So positive or negative findings don’t raise the post-test probability much at all, which is why we attribute this assessment a rather weak clinical value. Despite these findings, it’s still the best tool we have in physical assessment.

In the lower extremity nerve root compromise is most often seen on L4/L5 and L5/S1 level, followed by a far less incidence on L3/L4 and rarely on levels above that. Sensory testing for the lower extremity is done with the patient in supine and the lower extremity is exposed. Use a brush like the one found in the handle of most reflex hammers and stroke the dermatome regions on both the affected and unaffected limb and ask the patient whether they feel site-by-site differences.

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Other parts of the neurological examination of the upper limb are:

• Dermatome Testing (Upper Limb)
• Myotome Testing (Upper Limb)
• Reflex Testing (Upper Limb)

For the lower limb, the neurological examination can be studied here:

• Myotome Testing (Lower Limb)
• Reflex Testing (Lower Limb)

Al Nezari NH, Schneiders AG, Hendrick PA. Neurological examination of the peripheral nervous system to diagnose lumbar spinal disc herniation with suspected radiculopathy: a systematic review and meta-analysis. The Spine Journal. 2013 Jun 1;13(6):657-74.