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Dermatomal pain and parasthesia patterns exhibit significant overlap

PainSci » bibliography » Rainville et al 2016
Tags: diagnosis, back pain, neck, anatomy, neurology, pain problems, spine, head/neck

Four articles on PainSci cite Rainville 2016: 1. The Complete Guide to Low Back Pain2. Shin Splints Treatment, The Complete Guide3. The Complete Guide to Neck Pain & Cricks4. You Might Just Be Weird

PainSci commentary on Rainville 2016: ?This page is one of thousands in the bibliography. It is not a general article: it is focused on a single scientific paper, and it may provide only just enough context for the summary to make sense. Links to other papers and more general information are provided wherever possible.

Every spinal nerve root divides into a set of smaller nerves connected to a specific area of skin: a “dermatome,” the sensory distribution of a nerve root.

Numbness, and tingling within a dermatome are considered strong clinical clues that a particular nerve root is being squeezed or otherwise irritated. “Maps” of spinal nerve root innervation have always been illustrated and taught in the same way: distinctive and relatively precise spiralling patterns. The dermatome patterns most professionals are familiar with were established many decades ago, and were not studied much again until the 21st Century.

This study carefully checked the exact location of symptoms in 120 patients with suspected radiculopathy (symptoms in a dermatomal pattern, caused by nerve root compression). Perhaps unsurprisingly, they found that the dermatomal patterns were not as precise as the old maps would lead us to believe, and exhibit significant overlap, “to the extent that caution should be exercised when predicting compression of either the C6 or C7 nerve roots based on locations of impaired sensation.”

Pain and weird sensations from a troubled nerve root usually do not fill in the area of a dermatome precisely. Instead, they are filled in more like a child’s colouring book: lots of colouring outside the lines!

~ Paul Ingraham

original abstract Abstracts here may not perfectly match originals, for a variety of technical and practical reasons. Some abstacts are truncated for my purposes here, if they are particularly long-winded and unhelpful. I occasionally add clarifying notes. And I make some minor corrections.

BACKGROUND CONTEXT: Cervical radiculopathy is a common disorder caused by compression of the cervical nerve roots and is characterized by arm pain and altered sensory-motor function. Incongruity in the locations of C6 and C7 dermatomes in competing versions of historical dermatome maps has plagued interpretation of impaired sensation associated with C6 and C7 radiculopathies. Magnetic resonance imaging (MRI) allows accurate identification of the C6 or C7 nerve root compression and therefore makes it possible to explore sensory findings that are associated with compression of specific nerve root.

PURPOSE: This study compared the locations of impaired sensation in subjects with cervical radiculopathy from MRI-confirmed C6 and C7 nerve root compression.

STUDY DESIGN: Case series was used for this study.

PATIENT SAMPLE: A total of 122 subjects with symptoms suggestive of cervical radiculopathy were recruited by 11 spine specialist from 5 practice locations. Of these, 30 subjects had MRI-confirmed C6 and 40 subjects C7 radiculopathy.

OUTCOME MEASURES: Standardized pinprick sensory examination of the forearm and hand of every subject was performed, and the locations of sensory impairments were recorded.

METHODS: Sensory examination was performed before reviewing MRI results or performing motor or reflex examination. Areas of impaired sensation were recorded on drawings of the palmar and dorsal forearm and hand, and translated using a grid into 36 specific areas for analysis. Chi-square was used to compare frequencies of findings for each grid area for C6 and C7 radiculopathies. Power analysis suggested that a minimum of 27 subjects in each group were needed to detect a 30 percentage point difference in frequency of sensory impairments. Significance was set at ≤.05.

RESULTS: Approximately 80% of subjects had impaired sensation in at least 1 grid area, most often in the distal forearm and hand, and many had findings in multiple areas. There was nearly complete overlap for locations of impaired sensation for C6 and C7 radiculopathy, and the frequencies of impaired sensation differed only in the dorsal aspect of the distal radial forearm where it was twice as common in C6 radiculopathy (p=.02).

CONCLUSIONS: The location of sensory impairments associated with symptomatic C6 and C7 nerve root compression overlap to the extent that caution should be exercised when predicting compression of either the C6 or C7 nerve roots based on locations of impaired sensation. Impaired sensation in the radial aspect of the distal forearm is more common in C6 radiculopathies.

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