Serratus muscle stimulation effectively treats notalgia paresthetica caused by long thoracic nerve dysfunction: a case series

Charlie K Wang1, Alpana Gowda2, Meredith Barad1,2, Sean C Mackey1,2 and Ian R Carroll1,2*
*
Corresponding author: Ian R Carroll [email protected] Author Affiliations
1 Department of Anesthesia, Stanford University School of Medicine, Stanford Systems Neuroscience and Pain Lab, Palo Alto, CA, USA 2 Department of Anesthesia, Division of Pain Management, Stanford University School of Medicine, Stanford Pain Management Clinic, Redwood City, CA, USA
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Journal of Brachial Plexus and Peripheral Nerve Injury 2009, 4:17 doi:10.1186/1749-7221-4-17The electronic version of this article is the complete one and can be found online at: http://www.jbppni.com/content/4/1/17 Received:7 August 2009 Accepted:22 September 2009 Published:22 September 2009 © 2009 Wang et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
AbstractCurrently, notalgia paresthetica (NP) is a poorly-understood condition diagnosed on
the basis of pruritus, pain, or both, in the area medial to the scapula and lateral
to the thoracic spine. It has been proposed that NP is caused by degenerative changes
to the T2-T6 vertebrae, genetic disposition, or nerve entrapment of the posterior
rami of spinal nerves arising at T2-T6. Despite considerable research, the etiology
of NP remains unclear, and a multitude of different treatment modalities have correspondingly
met with varying degrees of success. Here we demonstrate that NP can be caused by
long thoracic nerve injury leading to serratus anterior dysfunction, and that electrical
muscle stimulation (EMS) of the serratus anterior can successfully and conservatively
treat NP. In four cases of NP with known injury to the long thoracic nerve we performed
transcutaneous EMS to the serratus anterior in an area far lateral to the site of
pain and pruritus, resulting in significant and rapid pain relief. These findings
are the first to identify long thoracic nerve injury as a cause for notalgia paresthetica
and electrical muscle stimulation of the serratus anterior as a possible treatment,
and we discuss the implications of these findings on better diagnosing and treating
notalgia paresthetica.
BackgroundNotalgia paresthetica (NP) is a poorly-understood condition presenting with pruritus,
pain, and paresthesias in an area medial to the scapula and lateral to the thoracic
spine. In addition, patients commonly report hyperpigmentation of the skin and other
skin abnormalities. It was first described by Astwazaturow in 1934, but both etiology
and prevalence of NP are unclear [1,2]. Previous authors have postulated the causes of NP include nerve entrapment of the
posterior rami of spinal nerves arising at T2-T6 [3-6], degenerative changes to the corresponding vertebrae [7], and possible involvement of a hereditary component [8]. Cutaneous innervation in this area is provided by the medial cutaneous branches
of the dorsal primary rami of the thoracic spinal nerves, which pass through muscles
stabilizing the scapula including the rhomboid and trapezius (Figure 1). Immunohistochemical investigations of the symptomatic area have been inconclusive
[9-11]. NP has been treated to varying degrees of success with a multitude of palliative
approaches directed specifically at the painful or pruritic skin, nerves, and muscle
medial to the scapula, including paravertebral nerve blocks [12], cervical epidural steroid injections [13], topical capsaicin [14,15], acupuncture [16], and botulinum toxin type A [17]. Systemic pharmacology used in neuropathic pain more generally has also been directed
at NP, including gabapentin [18] and oxcarbazepine [19]. With the exception of a trial of topical capsaicin reporting 30% relief of pruritus
[15], no long-acting treatment has shown efficacy in a RCT, and a divergence of explanations
for the etiology remains. There is a need to better understand and more effectively
treat NP.
Figure 1. Medial cutaneous branches of dorsal rami of spinal nerves, drawn in blue; Cutaneous
innervations of Notalgia Paresthetica area of presentation, with medial cutaneous
branches of dorsal rami of spinal nerves drawn in blue. Figure adapted from original in Color Atlas of Anatomy by Rohen and Yokochi, 2006.
The long thoracic nerve arises from branches of cervical nerve roots C5-C7 and innervates
the serratus anterior muscle. Injury to the long thoracic nerve or its cervical roots
leads to dysfunction of the serratus anterior, with consequent scapular winging or
loss of normal scapular protraction. We describe four cases of NP with known injury
to the long thoracic nerve or the cervical roots giving rise to the long thoracic
nerve, where transcutaneous electrical muscle stimulation (EMS) to the serratus anterior
in an area far lateral to the area of pain and pruritus (Figure 2) resulted in significant and rapid pain relief. These findings are the first to identify
long thoracic nerve injury with subsequent serratus anterior dysfunction as a cause
for NP and EMS of the serratus anterior as a possible successful conservative treatment.
Figure 2. Transcutaneous electrical muscle stimulation directly to the serratus anterior. Leads from a home electrical muscle stimulation unit on the lateral side of the scapula,
in the axilla and ventral to the lateral border of the latissimus dorsi, providing
EMS directly to the serratus anterior and far lateral from the area of pain and pruritus.
Case series presentationAll patients reported pain with or without pruritus between the thoracic spine and
medial scapula which grew progressively worse throughout the day. Furthermore, all
reported exacerbation with activities requiring forward flexion of the arms such as
driving, typing, washing dishes, or putting objects on a shelf. Patients did not report
skin abnormalities, and no hyperpigmentation was observed. When temperature sensation
in the area of maximal pain was tested with ice and compared to the contralateral
region, all patients reported reduced sensation of cold without frank numbness. All
had injury to the long thoracic nerve or the cervical roots at C5-7 giving rise to
the long thoracic nerve, despite the absence of clinically-apparent scapular winging.
There was no evidence of hyperpigmentation or other dermatologic symptoms. Prior to
treatment with EMS all patients had seen multiple physicians and physical therapists,
and tried multiple medications without relief. EMS of the serratus anterior muscle
was conducted at 70 Hz with a pulse width of 300 μs to induce tetany of the serratus
anterior. Stimulation was prescribed to be 30 seconds on and 30 seconds off for 15
minutes twice a day. All patients reported relief of pain beginning within days upon
starting EMS, recurrence of pain if they discontinued stimulation for any prolonged
period, and maintenance of analgesic effects with only intermittent stimulation necessary.
The patients described in this case series provided informed consent for the manuscript
and/or accompanying images to be published.
A 39-year-old male presented with pain and pruritus medial to the left scapula several
months after sustaining an ipsilateral broken clavicle and multiple rib fractures
in a bicycle accident. He reported a marked increase in pain with activity utilizing
his arms. Unlike his other pain complaints which improved following the accident,
over time his left mid-scapular pain became more persistent and refractory. At 60
mg of duloxetine his medial scapular pain was replaced by a sense of itching, and
then at 120 mg disappeared completely, although he ultimately could not tolerate duloxetine
due to “personality changes”. Electrodiagnostic studies revealed cervical root dysfunction
at C5, C6, and C7 suspected to be a traction injury from landing on his shoulder after
going over the handlebars of his bicycle. The patient began electrical stimulation
of the serratus anterior muscle in fall 2007. He reported using the stimulation approximately
15 minutes once a day. He discontinued using it after attaining significant relief
only to find that within several weeks the pain reappeared. Upon resuming intermittent
stimulation his pain relief returned. By follow-up email in April 2009, he characterized
his ongoing relief as “a highly significant improvement in the quality of my life….
Since I started to use [the stimulator] again I have been largely pain free”. Treatment
with muscle stimulation on an intermittent basis continues after 20 months follow-up.
A 52-year-old male presented with chronic right shoulder and mid-scapular pain and
pruritus of 20 years duration, status post ipsilateral thoracotomy and multiple shoulder
surgeries, the most recent of which was 2 years previous. The thoracotomy scar ran
perpendicularly across the expected path of the long thoracic nerve. He had failed
therapy with amytriptyline, valium, skelaxin, fentanyl, dilaudid, methadone, gabapentin,
and tizanidine. He reported no intercostal pain, and his notalgia paresthetica scapular
pain was located several inches medial to the posterior margin of the thoracotomy
scar. He began electrical stimulation of the serratus anterior muscle in July 2008.
In a follow up by email in April 2009, he reported pain relief as an “8 on a scale
of 10” and continues daily use of the stimulator. Follow-up after 9 months demonstrated
ongoing use of the stimulator and continuing relief.
A 40-year-old male physician presented with itching, paresthesias, and when symptoms
were severe, pain medial to the right scapula of 20 years duration, status post a
thoracotomy performed while a child. The ipsilateral thoracotomy scar ran across the
expected course of the long thoracic nerve. He reported no intercostal pain, and his
NP symptoms were located several inches medial to the posterior margin of the thoracotomy
scar. Past treatments included topiramate and over-the-counter analgesics. He reported
70% relief of symptoms within the first two weeks of using EMS to the serratus anterior
muscle and continues daily use as of September 2009. He continues to use the stimulator
intermittently after 9 months of follow-up.
A 34-year-old female presented with pain and pruritus medial to the right scapula,
status post cervical fusions of C4-5 and C5-6 in 2006 due to degenerative joint disease.
She also presented with neural foraminal stenosis in C6-7. Electrodiagnostic studies
were consistent with dysfunction of C5, C6, and C7. Nonetheless, she denied radicular
symptoms into the arms. Past treatments included gabapentin, desipramine, and multiple
opioids. Stimulation of the serratus anterior muscle began in fall 2007. As of April
2009 she uses the stimulation for 15 minutes a day but is only intermittently compliant.
When she discontinues stimulation the pain gets steadily worse prompting her to reinitiate
stimulation, and continue until improvement of symptoms once again leads to discontinuation.
Follow-up at 20 months following initiation of serratus stimulation revealed the patient
to be using the stimulator intermittently with continued benefit.
Discussion of findings and implications for etiologies of NPThe effectiveness of EMS, applied directly to the serratus anterior, in providing
significant pain relief supports our conclusion that notalgia paresthetica can be
caused by long thoracic nerve injury and consequent serratus anterior dysfunction.
These findings are the first to identify the association of long thoracic nerve and
serratus anterior dysfunction as a possible cause for NP, with EMS as a possible treatment.
Serratus dysfunction following long thoracic nerve injury and the resulting loss of
scapular protraction is well understood to lead to scapular winging. Although scapular
winging was not clinically apparent in these cases, subtle shoulder girdle asymmetry
was appreciated following knowledge of the diagnosis. We hypothesize that even in
the absence of obvious winging, loss of protraction may result in subtle retraction
of the scapula. This in turn may generate either traction or compression of the cutaneous
medial branches of the thoracic dorsal primary rami of spinal nerves as they course
to the skin through muscles attached to the non-protracted scapula such as the rhomboid
and trapezius. Traction on these nerves would be expected to refer pain to the area
between the scapula and the spine, the region of symptoms in NP.
This hypothesis would explain 1) the finding of long thoracic nerve and serratus anterior
dysfunction in patients presenting with pain medial to the scapula; 2) the finding
that the pain was exacerbated by activities with the arm flexed in front of the body,
which loads the serratus; 3) the loss of temperature sensation in the area of pain
medial to the scapular edge; 4) analgesia medial to the scapula in response to muscle
stimulation of the much more lateral serratus; and 5) previous reports of the efficacy
of anti-neuropathic pain medications such as gabapentin [18] and oxcarbazepine [19].
We suspect that EMS contracts the denervated serratus which is over-stretched under
the load of the arm in the chronic absence of physiologic contraction. The intermittent
contraction associated with the direct electrical muscle stimulation results in a
durable but ultimately reversible shortening of these overstretched muscle fibers
leading to a serratus muscle of shorter length, more closely approximating its normal
resting length. This shorter serratus muscle, while still unable to contract physiologically,
may nonetheless hold the scapula in a more anatomically correct position compared
to the completely stretched, unstimulated serratus seen following denervation. Further
work is needed to confirm or refute these speculations.
Our results are consistent with a case of NP and comorbid scapular winging reported
in 2004, in which NP naturally resolved several months before scapular winging [20]. Interestingly, in that case scapular winging preceded the onset of NP by several
months. In light of our findings, this suggests that both extent and duration of injury
to the long thoracic nerve are important factors in the pathology of NP. Our report
suggesting the efficacy of electrical serratus stimulation extends these observations,
and implies that serratus dysfunction is causally related to the pain, and not coincidental
to it.
Although our reports focus on long thoracic nerve and consequent serratus anterior
dysfunction as an etiology for the clinical syndrome of NP, it is possible that serratus
dysfunction is sufficient but not necessary. We have seen pain of similar presentation
among those with high thoracic disk disease, and in two patients with severe scoliosis
in whom the scoliosis appeared to result in impingement of the dorsal primary rami
between two adjacent transverse processes. Our experiences, along with radiographic
findings by others [5], also support spinal pathology as an alternative etiology of notalgia paresthetica.
Additionally, while serratus anterior dysfunction may lead to improper scapular stabilization,
an imbalance of other stabilizers such as the trapezius or other posterior scapular
stabilizers may provide the same symptoms. The authors suggest a defect in scapular
stabilization is just one of a variety of causes of irritation to the medial cutaneous
branches of the dorsal primary rami, yielding pain and pruritus in the region between
scapula and spine. This hypothesis on the pathophysiology of NP would predict that
the injury to other motor nerves stabilizing the scapula (e.g., the spinal accessory
nerve) or the stabilizing muscles they innervate might lead to a similar clinical
syndrome.
Our findings highlight the need to establish normal scapulothoracic stabilization
in patients presenting with NP. In cases of NP with a well-defined etiology of injury
to the serratus anterior, the long thoracic nerve, or the cervical roots it arises
from, EMS of the serratus anterior muscle may be a promising treatment modality for
notalgia paresthetica.
While pain and pruritus were both present in our patients, we note the lack of hyperpigmentation
or other visible skin abnormalities which commonly accompany descriptions of notalgia
paresthetica. It is unclear whether these skin abnormalities cause or are a result
of the pain and pruritus in the symptomatic area. Immunohistochemical findings in
NP have been inconclusive, with discordant conclusions on distributions of nerves
in the symptomatic area [9-11]. Further work is required to better characterize the relationship between pain, pruritus,
and hyperpigmentation, with knowledge that several distinct etiologies and consequent
presentations of notalgia paresthetica may exist. Compared to neuropathic pain, itch
is a commonly occurring, but less commonly appreciated, sequelae of nerve injury and
regeneration [21]. For example, itch is a significant symptom in more than 40% of patients with chronic
post herpetic neuralgia [22]. Two patients reported that their sense of itch was replaced by pain as symptoms
became more severe. One patient noted that duloxetine first made the pain transform
into an itch, and ultimately at a higher dose caused the sensation to resolve. Pain
and itch share similar underlying physiology [13]. A subset of substance P transmitting c-fiber neurons, similar to those implicated
in the pathogenesis of pain, has been associated with causing itch [23]. Stimulation of these neurons may directly lead to itch or itch may indirectly result
from mast cell degranulation caused by substance P [24,25]. Nonetheless, both dermatologists and neurologists may fail to recognize the neuropathic
nature of itch in some patients [13]. We speculate that even among patients whose sole manifestation of NP is itch, unlike
those in this case series, serratus anterior or long thoracic nerve dysfunction may
be to blame. Hyperpigmentation, occasionally noted in NP, may be a direct consequence
of neurologic dysfunction with neurogenic release of substance P in the skin which,
in addition to causing itch [23-26], also causes proliferation of keratinocytes, arterial smooth muscle cells, and fibroblasts
[27]. Alternatively, the neurologic dysfunction may result in hyperpigmentation indirectly
due to associated scratching, heat, or other stimuli applied to the dysesthetic skin.
We did not measure pruritus in a formal way before or following treatment and so the
efficacy in specifically reducing itch is not known. Future work will be of much greater
value and reliability if it includes formal measurement of itch severity before and
following treatment, which might include a Visual Analog Score (VAS) or another scale
of symptom severity.
It is possible that analgesia from electrical muscle stimulation is a result of transcutaneous
electrical nerve stimulation (TENS). A study investigating TENS for relief of NP symptoms
where TENS was applied to the symptomatic area medial to the scapula found roughly
30% improvement in pruritus over two weeks [28], highlighting the need to account for TENS-induced analgesia in any randomized blinded
trial by including a TENS control arm. We feel it is unlikely that the analgesia from
electrical nerve stimulation provided here was due to a TENS-like effect for three
reasons: 1) the area of stimulation on the serratus, on the lateral side of the scapula
in the axilla and ventral to the lateral border of the latissimus dorsi (Figure 2), was far removed from the area of pain; 2) pain relief was not apparent during stimulation,
relief followed after several days of the treatment, and persisted for several days
with only intermittent stimulation and, perhaps most convincingly, 3) several patients
required fine adjustment in the placement of the stimulating pads to elicit contraction
of the serratus anterior rather than the latissimus dorsi. This minute adjustment
in pad placing, moving further away from the site of pain as the pads were shifted
anteriorly to avoid the latissimus, made the difference between ineffective and effective
stimulation. If the effect were due to a TENS-like effect or a placebo effect, the
efficacy of the intervention would not be expected to differ so dramatically based
on fine adjustments of pad placement far lateral to the site of pain.
We describe a novel and well-defined etiology of long thoracic nerve injury with consequent
serratus anterior dysfunction in notalgia paresthetica, and EMS of the serratus anterior
as a long-acting and effective treatment conferring the advantage of a once-daily
treatment regimen. Future work might expand on this case series by: 1) conducting
randomized blinded trials of serratus stimulation for NP; 2) conducting case-control
studies among patients with NP to evaluate the association of NP and long thoracic
nerve injury; 3) performing quantitative sensory testing (QST) to document the presence
of nerve injury in the area of pain among patients with NP and potential QST improvements
after treatment; and 4) exploring if loss of scapular stabilization by other means,
e.g. injury to the dorsal scapular nerve and spinal accessory nerve, leads to a similar
clinical syndrome with respect to NP. We also note that future studies of notalgia
paresthetica would benefit immensely from a multidisciplinary approach integrating
the expertise of dermatologists, neurologists, orthopedic surgeons, and pain management
specialists.
ConclusionNotalgia paresthetica is a poorly-understood condition in which patients present with
pain with or without pruritus and paresthesias in an area lateral to the spine and
medial to the scapula. To date, there have been various proposed etiologies of NP
and a multitude of different treatment approaches which have met with varying degrees
of success. We describe a novel and well-defined etiology of long thoracic nerve injury
with consequent serratus anterior dysfunction in notalgia paresthetica, and EMS of
the serratus anterior as a long-acting and effective treatment conferring the advantage
of a once-daily treatment regimen. The authors hypothesize that abnormal scapulothoracic
stabilization creates traction or compression of the cutaneous medial branches of
the thoracic dorsal primary rami. This then gives rise to the symptoms of this syndrome.
EMS of the serratus anterior muscle is a possible treatment for NP that deserves further
study.
Competing interestsThe authors declare that they have no competing interests.Authors’ contributionsAG conducted all electrodiagnostic studies and treated patients clinically. IRC treated
patients clinically. MB and SM helped with manuscript preparation, literature review,
and background context for the manuscript. SM additionally provided material resources.
CKW led the literature review and prepared the manuscript. All authors critically
read and approved the final manuscript.
AcknowledgementsWe would like to acknowledge David Mull for teaching the correct application of the
EMS unit to each of the patients in this case report.
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