Introduction to a Referred Sympathetic Pain Map
This paper presents a description of a unique and previously unde-scribed map of referred sympathetically-mediated pain. The mapping is based upon pain relief with selective nerve root procedures, primarily within the thoracic spine. The mechanism for their efficacy is hypothesized to be via the sympathetic afferents, which travel through the dorsal root ganglion (DRG).
In a manner similar to a dermatomal map, each spinal cord segmental level from T1 to L2 is described as having a specific region of the body that it innervates, with each level identified using the newly-coined term “fibromatome.” The map is meant to supplement the radicular and peripheral nerve maps and to be applied in cases in which these maps do not apply or when the response to treatments for radicular or peripheral nerve pain are ineffective. Notably, the fibromatome map is unique in that at certain levels patients can develop almost hemi-body symptoms, and can account for pain complaints that are currently described as non-physiological. An understanding of fibromatomes may allow spine physicians to synergistically treat these conditions both pharmaceutically and interventionally.
This concept was initially discovered after a number of patients who had undergone thoracic spine epidurals reported unex-pected relief of symptoms such as extremity pain or headaches. A classic example of this phenomenon is illustrated in Figure 1. The patient is a 37-year-old disabled gentleman with widespread pain diagnosed as vasculitic arthritis, who subsequently had significant relief of all of his widespread pain with thoracic nerve root procedures. The pain drawings, before and after the first two thoracic epidural steroid injections (TESIs), clearly indicate widespread relief of all left sided pain (notably, the right-sided pain was initially worse).
Because these epidurals typically produced a warm/hot sensation (similar to a sympathetic block) and were located within the thoracic spine, I reasoned that they were affecting sympathetically-med-iated pain. Over time, I recognized that these procedures positively affected complaints mediated by the autonomic nervous system—such as sinus congestion, reactive airway disease, IBS and bladder dysfunction, thermoregulatory dysfunction, Raynauds, and peripheral edema. This strengthened my belief that I was treating sympathetically-mediated pain. While these epidurals were the impetus to my current work using nerve root procedures, it is important to note that, as a treatment, they are problematic and may cause increasing pain if done without proper training.
I have defined fibromatomes as specific regions of referred sympathetic pain depending upon the level of the spine affected. The term fibromatome is analogous to dermatome. While a dermatomal pain pattern refers to the region innervated by the sensory afferents via a specific dorsal root ganglion, a fibromatomal pattern refers to the region of referred pain innervated by the sympathetic afferents that enter via a specific dorsal root ganglion (see Figure 2). Notably, although the initial work was done in fibromyalgia patients (hence the term fibromatomes), many patients without fibromyalgia will have similar pain generators (see case reports).
In much the same way as a patient presenting with low back pain radiating down the lateral leg to the dorsal foot that is completely relieved with a L5 nerve block has pain in an L5 dermatome; a patient with unexplained calf pain, (often associated with anterior thigh pain) which is completely relieved with a T9 nerve root procedure would be considered to have pain in a T9 fibromatome. Notably, this description of the T9 fibromatome is based upon a series of patients being successfully treated (i.e. 95+% relief for at least one month) for similar symptoms with T9 nerve root procedures. As the examples below indicate, these procedures have been done in patients with a variety of complaints and, even when successful, only treat specific regions of pain.
Example 1. A 50-year-old woman with generalized pain (i.e. severe fibromyalgia) presents with a chief complaint of left anterior thigh and posterior calf pain. Patient has radiological rotational/scoliotic abnormalites and tenderness to palpation at T9. Left T9 selective nerve root block (SNRB) provides the patient with 10 months of relief in the T9 fibromatome distribution (i.e. anterior thigh and posterior calf). All other pain remained stable following the SNRB.
Example 2. A 60-year-old gentleman with failed lumbar spine syndrome and intractable low back pain secondarily complains of a 50-year history of left (more so than right) calf pain (he had fallen off a roof when he was 10 years old). Patient has radiological rotational/scoliotic abnormalites (see Figure 3) and tenderness to palpation at T9. Left T9 SNRB provides the patient with 8 months of calf pain relief. A Left T9 pulsed radiofrequency of the dorsal root ganglion (PRFDRG) performed 4 months ago has provided the patient with no recurrence of calf pain. Low back pain remains severe.
Understandably, this concept seems completely unique. However, I would like to point that all of us accept that cardiac ischemia often refers pain to the arm, neck, jaw, etc., and therefore already accept a phenomenon very similar to the concepts described in this paper. Basic science research that is consistent with a similar mechanism includes studies showing cardiac ischemia causes increased amplitude on EMG over T4-5 in dogs,2 and that myocardial ischemia is mediated by sympathetic afferents in cats.3
As described in the above examples, there are often notable scoliotic and/or rotational changes at affected levels (usually within the thoracic spine). Notably, these skeletal abnormalities are oftentimes much more impressive than underlying cervical and lumbar spine dysfunction which are not easily seen using plain x-rays. These abnormalities can be very impressive such as in Figure 4a, a patient who was told by repeated doctors that she should not have widespread pain because there was nothing wrong with her. Figure 4b illustrates her initial pain diagram (pre-) and a recent post-treatment diagram after undergoing a number of thoracic spine procedures.
These maps were developed by evaluating pain diagrams before and after selective nerve root blocks (at least 1 to 2 weeks) and, more recently, pulsed radio-frequency of the dorsal root ganglion. Notably, the latter method—being more effective, less painful, much safer and technically easier—is the only method I currently use. Also, of note at the level in which the DRG/SNRB is performed, I have been doing medial branch block procedures but have come to believe it is the former procedure that is providing the greater amount of relief. In regards to the validity of this map from an interventional spine perspective, the author would like to reiterate or point out the following observations: