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 Table of Contents  
Year : 2018  |  Volume : 32  |  Issue : 2  |  Page : 72-75

2–4 mm diameter hypo/depigmented dermal spots: ? Objective sign of somatic origin pain

Doshi Pain Relief Centre, In-Charge Pain Clinic- Jupiter, Bethany Hospitals, Thane, Maharashtra, India

Date of Web Publication31-Aug-2018

Correspondence Address:
Dr. Kritika Doshi
202, 1B, Varun Arcade, Lawkim, Thane 400 610
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijpn.ijpn_69_17

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It is known that somatic nerves are affected by pathological changes occurring in the corresponding intervertebral discs. However, there is as yet no serological test or biomarker to diagnose disc pathology. A recurring observation in patients reporting to the Pain Clinic was the presence of discrete, 2-4 mm in diameter, hypo/de-pigmented spots on the skin. Is there a probable explanation to the occurrence and location of these hypo/depigmented spots? When co-related to the MRI of the spine, these spots (KD Spots) were frequently seen to lie in the dermatome corresponding to the degenerated intervertebral disc. Based on the experimental and clinical reports in scientific literature and the observation of the author a hypothesis to explain the presence of the hypo/depigmented spots in relation to degenerated intervertebral discs is proposed.

Keywords: Hypopigmented spots, KD spots, objective sign, somatome

How to cite this article:
Doshi K. 2–4 mm diameter hypo/depigmented dermal spots: ? Objective sign of somatic origin pain. Indian J Pain 2018;32:72-5

How to cite this URL:
Doshi K. 2–4 mm diameter hypo/depigmented dermal spots: ? Objective sign of somatic origin pain. Indian J Pain [serial online] 2018 [cited 2020 Jul 15];32:72-5. Available from: http://www.indianjpain.org/text.asp?2018/32/2/72/240291

  Introduction Top

Pain is underreported, underdiagnosed, and undertreated. One of the contributing factors for the underdiagnosis of pain is the lack of objective signs in chronic pain. While examining patients reporting to the pain clinic, it was seen that they showed the presence of discrete, 2–4 mm in diameter, hypo/depigmented spots on the skin. This was a recurring observation in patients reporting various complaints of somatic pain. When correlated to the magnetic resonance imaging (MRI) of the spine, these were seen to lie in the dermatome corresponding to the degenerated intervertebral disc. It is known that the somatic nerves are affected by pathological changes occurring in the corresponding intervertebral discs.[1]

  Description of the “Spots” Top

These spots were seen to be discrete, 2–4 mm in diameter, hypo/depigmented, varying in number, without raised margins, nontender, and innocuous [Figure 1]. These spots were easily seen in the patients because of the contrast between the pigmented skin and the hypopigmented spots. These were also present in a dermatomal distribution.
Figure 1: Obvious hypopigmented spot on skin, 2–4 mm in diameter

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Why were these spots evident in certain areas, whereas absent in other parts of the body including the corresponding contralateral side of the patient? As yet no report of similar observations is available. As this is a completely new coincidental finding, in this article, they will be termed as “KD spots.” I would like to present this observation and suggest a hypothesis to explain the distribution of these spots.

  Collection of Observational Data Top

From 2007 to 2016, 1000 patients (nonconsecutive) reporting to the outpatient department of the pain clinic with KD spots were seen. Of these, 710 patients had MRI scanning carried out for their complaints of pain. MRI was not essential for remaining 290 patients and was not suggested. The patients who refused to be photographed were not included.

The MRI scans were correlated to the patients who had these visible spots so as to look for any evidence of a probable prediction and identification of somatic pain in a dermatomal distribution (KD spots). The patients (710) who presented had complaints of the following [Table 1]:
Table 1: Summary of observations

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  1. Back, neck pain with/without radicular arm/leg pain (378)
  2. Postsurgical pain (185)
  3. Abdominal pain (48)
  4. “Tennis” elbow (21)
  5. Cancer pain (78)

The patients themselves were unaware of the presence of these spots and were examined by a dermatologist to rule out other possible causes of hypopigmentation such as tinea versicolor, pityriasis alba, idiopathic guttate hypomelanosis, post-inflammatory hypomelanosis, atopic dermatitis, and psoriasis.

  Observations Top

The KD spots seen in these patients were hypo/depigmented, present as discrete, round spots, and had a consistent diameter of 1–4 mm, irrespective of variation in height, weight, or age of the patient [Figure 2]. The number of spots varied from 1 to 15–20 with older patients showing more numerous spots in each affected dermatome. They were seen to be present in all areas (cervical to sacral region).
Figure 2: Magnified view of KD spot. Black arrow pointing to 4X magnified KD Spots

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The time of initial onset of the spots was unknown as the patients were not aware of the spots. They could have been present for a variable time; they were present in the painful dermatomal areas and were also seen in non-symptomatic areas in few patients. Only two female patients had noticed the spots as they were visible on the arm surface. The youngest patient on whom the spots were visible was aged 19 years. A surprising observation was that the spots in these patients were corresponding to the degenerative disc disease as seen on their MRI scans [Figure 3] and [Figure 4].
Figure 3: (A) T2W MRI Axial image of D11-12 with annular tear (on left). (B) KD Spots seen on left D11/12 dermatomal area

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Figure 4: (A) MRI - Cervical Degenerative Disc Disease. (B) Visible KD Spots on Right C5, C6 dermatomes. (C) Visible KD Spots on Left C5, 6 dermatomes. (D) T2W MRI showing degenerative changes in L4-5, L5-S1 discs with lateral canal narrowing. (E) KD Spot (yellow arrow) over S1 dermatome area. (F) KD Spot (yellow arrow) on Right Lower limb ventral Surface (L4 dermatome) and Left Lower limb dorsal surface (L5/S1 dermatome)

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Dermatomal distribution of KD spots:

  1. Back/neck and limb pain: 328/378 patients (86.7%) had visible spots in the corresponding dermatome of the involved intervertebral disc as seen on MRI scans.
  2. Postsurgical pain: 112/185 patients (80.51%) with pain after surgery had visible KD spots.

    1. Inguinal hernia: visible KD spots in T12-L1 distribution
    2. Cholecystectomy: visible KD spots in T8 dermatome
    3. Lower section cesarean section: visible KD spots in T12, L1 dermatome
    4. Total knee replacement: visible KD spots in L2, L3, and L4 dermatomes
    5. Spine surgery: visible spots ventrally and dorsally over L2-L3-L4-L5

  3. Abdominal pain: 30/48 patients had these spots on the abdominal dermatomes. All of them had been investigated to rule out other causes of visceral pain.
  4. “Tennis elbow”: 10/21 patients with a diagnosis of tennis elbow had KD spots in the C4-C5-C6-C7 dermatomal distribution.
  5. Cancer-related pain: 60/78 patients with cancer had KD spots in different parts of the body surface.

  Discussion Top

A somatome is a field of somatic and autonomic innervation based on the segmental embryologic expression of the somatic tissues.[2] A complete somatome is composed of the dermatome, the myotome, and the sclerotome.

There is evidence in literature that the somatic nerves can be affected by pathological changes occurring in the intervertebral discs and the ensuing neuroinflammatory cascade.

  1. Hause[3] has reported that the disc pathology may precede clinical radicular symptoms.
  2. MacMillan et al.,[4] McCarron et al.,[5] and Nygaard et al.[6] have speculated that the leakage of nociceptors from the disc (nuclear material) sensitizes the C or A delta unmyelinated nerve fibers in the annulus and the dorsal root ganglion (DRG), lowering the nociceptor threshold for mechanical stimulation.
  3. Yamashita et al.[7] have proved that the sensitization of nociceptive spinal neuronal responses develops quickly following exposure of the DRG to NP (nucleus pulposus) and that the exposure to inflammatory mediators in NP causes long-lasting degeneration of DRG neurons.
  4. Cuellar et al.[8] have shown that the chemical sensitization of DRG neurons occurs with the release of nociceptive substances by the disc.
  5. Kobayashi et al.[9] have reported that the dysfunction in patients with nerve root compression because of lumbar disc herniation or lumbar canal stenosis is not confined to the degeneration at the site of compression but also extends to the primary sensory neurons within the DRG as a result of the axon reaction.

References in scientific literature about “spotlike cutaneous receptor fields” are as follows:

  1. It has been reported by Christenson and Perl in1970 and Schouenborg and Sjolund in 1983 that many neurons driven by C fibers in laminae I and II have small receptive fields on the skin. Bessou and Perl[10] reported that the receptive field of low-threshold C mechanoreceptors was an area of 2–6 mm2.
  2. Various studies have defined the receptive field properties of unmyelinated tactile afferents in the human skin:

    1. Liljencrantz and Olausson[11] have reported that the receptive field of a human tactile C-afferent fiber is round or oval in shape with no preferred orientation, and it consists of 1–9 small responsive hot spots distributed over an area up to 35 mm2.
    2. Kumazawa and Mizumura[12] observed that the receptive area of polymodal receptors was spotlike and appeared to be located not only on the surface but also in the midst of the muscle in their study of skeletal muscle of dogs.
    3. Lynn and Carpenter,[13] in 1982, reported that the diameter of the cutaneous receptive field on the hind limb of a nociceptive C-afferent fiber is small in the rat, usually less than 2 mm.
    4. Wessberg et al.[14] reported that the individual field of cutaneous mechanoreceptive afferents with conduction velocities in the C range consisted of one to nine small responsive spots distributed over an area of 1–35 mm2.

The findings in the abovementioned references very much correlate with the observation of the spots on the corresponding dermatome of the affected intervertebral disc (somatome involved). The distribution of KD spots in back and limb pain is 86.77%. Further studies in a larger cohort would help to prove the sensitivity and specificity of it.

I would like to propose the following hypothesis to explain the presence of the KD spots:

An initiating event in the intervertebral disc causing leak of nuclear material and/or disc disruption would stimulate an inflammatory process with sensitization of corresponding DRG neurons and the somatic nerve with resultant distal effects on the somatome. The myotome would develop latent myofascial trigger points as a result of sensitization of muscle nociceptor afferent. The dermatomal spots would correspond to the receptive field of polymodal C-afferent fibers. Hypo/depigmentation maybe a result of apoptosis/cellular destruction of cell body secondary to immunologic/inflammatory events following leakage of nuclear material. (The loss of pigmentation could reflect a neurogenic/humoral mechanism involving the sympathetic system similar to hyperpigmentation seen in complex regional pain syndrome).

  Note Top

Can these spots indicate an early objective sign of disc pathology? Can these be used as an early predictive sign of internal disc damage and ongoing dysfunction and chemical sensitization at the DRG or motor rootlets?

This is a coincidental observation–consideration of these spots as an early predictive sign of internal disc disease and ongoing dysfunction and chemical sensitization at the DRG or motor rootlets need to be confirmed with further studies.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.


I would like to thank Dr. R. P. Gehdoo for the assistance with the scripting of the initial article.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Weinstein JN. Mechanism of spinal pain. The dorsal root ganglion and its role as a mediator of low back pain. Spine 1986;11:999-1001.  Back to cited text no. 1
Jinkins JR, Whittemore AR, Bradley WG. The anatomic basis of vertebrogenic pain and the autonomic syndrome associated with lumbar disk extrusion. AJNR 1989;10:219-31.  Back to cited text no. 2
Hause M. Pain and the nerve root. Spine 1993;18:2053.  Back to cited text no. 3
MacMillan J, Schaffer JL, Kambin P. Routes and incidence of communication of lumbar discs with surrounding neural structures. Spine 1991;16:167-71.  Back to cited text no. 4
McCarron RF, Wimpee MW, Hudkins PG, Laros GS. The inflammatory effect of nucleus pulposus. A possible element in the pathogenesis of low back pain. Spine 1987;12:760-4.  Back to cited text no. 5
Nygaard OP, Mellgren SI, Osterud B. The inflammatory properties of contained and noncontained lumbar disc herniation. Spine 1997;22:2484-8.  Back to cited text no. 6
Yamashita M, Ohtori S, Koshi T, Inoue G, Yamauchi K, Suzuki M, et al. Tumor necrosis factor-alpha in the nucleus pulposus mediates radicular pain, but not increase of inflammatory peptide, associated with nerve damage in mice. Spine 2008;33:1836-42.  Back to cited text no. 7
Cuellar JM, Montesano PX, Carstens E. Role of TNF-alpha in sensitization of nociceptive dorsal horn neurons induced by application of nucleus pulposus to L5 dorsal root ganglion in rats. Pain 2004;110:578-87.  Back to cited text no. 8
Kobayashi S, Yoshizawa H, Yamada S. Pathology of lumbar nerve root compression. Part 2: morphological and immunohistochemical changes of dorsal root ganglion. J Orthop Res 2004;22:180-8.  Back to cited text no. 9
Bessou P, Perl ER. Response of cutaneous sensory units with unmyelinated fibers to noxious stimuli. J Neurophysiol 1969;32:1025-43.  Back to cited text no. 10
Liljencrantz J, Olausson H. Tactile C fibers and their contributions to pleasant sensations and to tactile allodynia. Front Behav Neurosci 2014;8:37.  Back to cited text no. 11
Kumazawa T, Mizumura K. Thin-fibre receptors responding to mechanical, chemical, and thermal stimulation in the skeletal muscle of the dog. J Physiol 1977;273:179-94.  Back to cited text no. 12
Lynn B, Carpenter SE. Primary afferent units from the hairy skin of the rat hind limb. Brain Res 1982;238:29-43.  Back to cited text no. 13
Wessberg J, Olausson H, Fernström KW, Vallbo AB. Receptive field properties of unmyelinated tactile afferents in the human skin. J Neurophysiol 2003;89:1567-75.  Back to cited text no. 14


  [Figure 1], [Figure 2], [Figure 3], [Figure 4]

  [Table 1]


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