Nuances of Spinal

Radiculopathy

James Mallows

Spinal dermatomes

• A dermatome is an area of skin that is

mainly supplied by a single spinal nerve

History of dermatomes

• Pioneering work by Sherrington (late

19th century), Foester (1933) and

Keegan and Garrett (1948)

• Based on multiple animal experiments

and clinical situations

History of dermatomes

• Sherrington

• Study in monkeys

• Severed multiple spinal nerves above

and below a single spinal nerve and

mapped the sensory supply of that

nerve

• Found very predictable dermatomes

History of dermatomes

• Other clinical data

• Herpes zoster

• War injuries

• Spinal root injections with local anaesthetic

• Human dermatomal maps varied little from

the animal models

Dermatomes

• Most areas of the skin are innervated by

2 or more spinal nerve roots

• Also get intrathecal intersegmental

anastomoses of dorsal spinal rootlets,

allowing sensory neurons at one dorsal

root ganglion to enter the spinal cord at

a different level

Dermatomes

• Thus a single spinal nerve lesion may

not cause noticeable sensory loss,

especially in the trunk

• However in the limbs, complete

interruption of a single peripheral nerve

produces changes in sensation that are

often appreciated by a patient

Diagnosis of radiculopathy

• Clinical decisions are made by

correlating a patient’s symptoms and

imaging with sensory dermatomal maps

• Assumption is that pain and

paraesthesias will follow the same

dermatomal distribution

Dynatomes

• We are now gaining an understanding

of pain distribution in spinal

radiculopathy

• Dynatomes vs dermatomes

• A dynatome is an area of skin that can

experience pain in pathology of a

particular nerve root

Dynatomes

• Slipman CW, Plastaras CT, Palmitier

RA et al. Symptom Provocation of

Fluoroscopically Guided Cervical Nerve

Root Stimulation. Spine 1998;23:2235-

2242.

Slipman et al

• To document the distribution of pain and

paraesthesia that result from stimulation

of specific cervical nerve roots and

compare that to documented

dermatomal maps

Slipman et al

• Consecutive patients undergoing

fluoroscopically guided cervical nerve

root blocks (C4-C8)

• Immediately preceding contrast

injection, mechanical stimulation of the

nerve root was performed

• The site of the pain experienced was

recorded and mapped

Slipman et al

• 134 nerve root stimulations on 87

patients

Slipman et al

• Distinct differences between dynatomal

and dermatomal maps

Dynatomes

• Murphy DR, Hurwitz EL, Gerrard JK and

Clary R. Pain patterns and descriptions

in patients with radicular pain: Does the

pain necessarily follow a specific

dermatome? Chiropractic & Osteopathy

2009;17.

Murphy et al

• To describe the distribution of pain in

patients with cervical and lumbar

radicular pain

• All patients either had:

• disc protrusion or lateral canal stenosis

demonstrated on complex imaging; or

• EMG documentation of nerve root

dysfunction

Murphy et al

• Used a variety of manoeuvres to elicit

spinal root pain

• Patient then mapped where they

experienced their pain

• This map was compared to standard

dermatomal charts and was classified

as either dermatomal or non-

dermatomal

Murphy et al

• 226 nerve roots in 169 patients

• Pain was non-dermatomal in 69.7% in

cervical radiculopathy and in 64.1% in

lumbar radiculopathy

• However in S1 radiculopathy, 64.9% of

pain was dermatomal

Murphy et al

• In most cases nerve root pain should not

be expected to follow along a specific

dermatome, and a dermatomal distribution

of pain is not a useful historical factor in

the diagnosis of radicular pain. The

possible exception to this is the S1 nerve

root, in which the pain does commonly

follow the S1 dermatome

Dynatomes

• Possible reasons

• Referred pain from discs or other tissues

• Overlaps between dermatomes

• Intense and persistent nociceptive input

can expand the size of the receptive fields

of those dorsal horn cells

Dynatomes

• Therefore we must beware the classical

teaching of being able to correlate a

patient’s pain distribution to the

dermatomal nerve root of the site of the

pain

Epidural steroid injections

• Do they work?

• Everyone seems to do them

• “I don’t know, I work in emergency”

• “I’m booked in for one next week but I

just can’t wait for it”

Epidural steroid injections

• Shamilyan TA, Staal JB, Goldman d,

Sands-Lincoln M. Epidural steroid

injections for radicular lumbosacral pain:

a systematic review. Physical Medicine

and Rehabilitation Clinics of North

America. 2014;25:471-89.

Shamilyan et al

• Most guidelines do not recommend

routine use of epidural steroid injections

• Small short term but not long term

improvement in leg pain and function

• Evidence does not support routine use

of off-label epidural steroid injections

Epidural steroid injections

• Quraishi NA. Transforaminal injection of

corticosteroids for lumbar radiculopathy:

a systematic review and meta-analysis.

European Spine Journal. 2012;21:214-

219.

Quraishi

• 126 papers: 5 RCTs with 3 following up

patients for more than 3 months

• 187 patients in the treatment group and

181 in the control group

Quraishi

• Improvement of pain but not disability

was observed in the treatment group

but not statistically significant

Epidural steroid injection

• Carmel A, Argoff CE, Samuels J,

Backonja M-M. Assessment: Use of

epidural steroid injections to treat

radicular lumbosacral pain. Neurology

2007;68:723-729.

Carmel et al

• Report of the Therapeutics and

Technology Assessment Subcommittee

of the American Academy of Neurology

Carmel et al

• Epidural steroid injections may result in

some improvement in radicular

lumbosacral pain when assessed

between 2 and 6 weeks following the

injection, compared to control

treatments (Level C, Class I–III

evidence)

Carmel et al

• Epidural steroid injection for radicular

lumbosacral pain does not impact

average impairment of function, need

for surgery, or provide long-term pain

relief beyond 3 months. Their routine

use for these indications is not

recommended (Level B, Class I–III

evidence)

Carmel et al

• There is insufficient evidence to make

any recommendation for the use of

epidural steroid injections to treat

radicular cervical pain

Epidural steroid injections

• Cohen SP, Hanling S, Bicket MC et al.

Epidural steroid injections compared

with gabapentin for lumbosacral

radicular pain: multicentre randomized

double blind comparative efficacy study.

BMJ 2015;350:h1748.

Cohen et al

• 145 people with lumbosacral radicular

pain secondary to herniated disc or

spinal stenosis for less than four years

in duration and in whom leg pain is as

severe or more severe than back pain

Cohen et al

• Participants received either epidural

steroid injection plus placebo pills or

sham injection plus gabapentin

• A positive outcome was defined as a ≥2

point decrease in leg pain coupled with

a positive global perceived effect

Cohen et al

• Average reduction in pain scores

• 1 month

• Steroids -2.2 (SD 2.4) gabapentin -1.7 (SD 2.6)

(p=0.25)

• 3 months

• Steroids -2.0 (SD 2.6) gabapentin -1.7 (SD 2.7)

(p=0.43)

Cohen et al

• Gabapentin and epidural steroid

injections used to treat lumbosacral

radicular pain both resulted in modest

improvements in pain and function,

which persisted through three months

Cohen et al

• Although some differences favoured

epidural steroid injections, these tended

to be small and transient (and not

significant)

• Similar outcomes between treatment

groups suggest a trial with neuropathic

drugs might be a reasonable first line

treatment option

Cohen et all

Likely causes

1. The treatments are equally effective but

the effect dissipates over time

2. Neither treatment is effective ie placebo

response or natural course of the disease

3. Epidural steroid injections are superior to

gabapentin but sample was too small

Cognitive error

• Commission bias

• Tendency toward action when the evidence

supports inaction

• Illusory correlation

• When 2 actions coexist but are not directly

related to each other

• “I got a steroid injection and the pain got a lot

better” [but then it got worse and I had to have

another one]

Thank you