What is a dermatome?
If you have pain referred from an area in your spine – you have probably heard of the word dermatome.
In physiotherapy – we refer to two types of “tomes” – dermatomes and myotomes.
In our spine we have 7 cervical vertebrae (neck), 12 thoracic vertebra (mid-back), 5 lumbar vertebra (lower back) and 5 sacral vertebrae (near the tail bone – these sacral vertebrae are fused together). At each spinal level, nerves exit from the spinal cord. We call these different levels C1, C2, T3, L5 etc etc.
Dermatomes describe where a spinal level innervates the skin.
Myotomes describe which muscle the spinal level innervates.
A time when dermatome testing comes in use during physiotherapy is during an assessment. Some clients will attend physiotherapy with a shoulder problem, with pain which travels down their arm. Although some shoulder issues can refer into the top of the arm (near the deltoid) it would be unlikely that the pain would travel down to the wrist. This would have your physiotherapist thinking – it is less likely to be a shoulder issue and perhaps is coming from the neck (eg C6). Dermatomal mapping has changed over the years, with each scientist investigating it getting a slightly different map. For more information on the progression of dermatomal mapping over the centuries, Downs and Laporte (2011) wrote an article called “conflicting dermatome maps: educational and clinical implications” – which talks through the different maps over the years.
Myotomes are of interest to your physiotherapist when you are having loss of strength in a muscle. Eg you are unable to stand up on your toes or unable to grip, and your muscles simply cannot produce the force required. This loss of strength can happen from muscle injury or tear, or it can be of spinal origin. Strength loss or giving way is often an alarm bell for physiotherapists and we will refer on for further testing.
This is why your physiotherapist asks you to do so many different movements and tests in an assessment, as well as asking you many questions about how your pain started and how it has progressed. Nerve conduction testing is another way to assess if there is a deficit how your nerves are sending their measurements. Sometimes a problem with a nerve occurs at the root – eg at the spine. Other times it can occur down the chain eg for the arm, the nerve problem may be in the neck, the shoulder, the elbow or the wrist. For this kind of case, nerve conduction testing can give a more clear diagnosis. An example of this would be a client with arm and wrist pain, in which the doctor and physiotherapist are unsure whether the pain is coming from the neck, or from the wrist (carpal tunnel). Nerve conduction testing can give a clear answer on this.
Emily Georgopolous (APAM)
Masters of Physiotherapy
Featured in the Top 50 Physical Therapy Blog
- Downs, MB & Laporte, C 2011, ‘Conflicting dermatome maps: educational and clinical implications.’, The Journal of Orthopaedic and Sports Physical Therapy, vol. 41, no. 6, pp. 427–434.