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The concept of dermatomes came from early attempts to correlate the physiology of sensation with anatomy. There are various definitions of dermatomes and several maps in common use. While useful, dermatomes are subject to considerable variation between maps and, indeed, between individuals. Anecdotally, precise dermatome distributions are generally regarded by experienced neurologists with a degree of caution, being viewed as an approximation. In this article, we consider the validity of the dermatome maps and their background, as well as introducing a relatively recent ‘evidence based’ dermatome map.
Dermatomes and their significance
Localisation of sensory symptoms and signs to specific parts of the central and peripheral nervous systems is a significant part of the neurological examination and diagnostic evaluation—the crucial ‘where is the lesion?’ question. Ever since the first attempts at mapping dermatomes in the late 19th century, neurologists have used dermatomes in their clinical diagnosis of radiculopathy and in determining the level of spinal cord injury. Neurosurgeons and neurophysiologists rely on dermatomes for intraoperative monitoring of spinal cord function through somatosensory evoked potentials. And reliance is also placed on dermatomes in the practice of regional anaesthesia.
The concept of dermatomes originated in early attempts to correlate the physiology of sensory experience with an anatomical substrate. Today, the term ‘dermatome’ generally refers to an area of skin innervated by a particular neural element, specifically nerve root, dorsal root ganglion or spinal segment. Dermatomes are of course distinct from the areas of skin supplied by particular peripheral nerves, these often referred to as the peripheral nerve fields (or cutaneous nerve distributions). Despite the long tradition, and the emphasis still placed on teaching dermatomes to medical students, experienced neurologists, perhaps because they are well aware of the ‘approximate nature’ of the various maps, probably attach rather less significance to the precise dermatome distribution than the corresponding myotomes …
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