Indian Journal of Dental Research

: 2011  |  Volume : 22  |  Issue : 5  |  Page : 678--683

Changes in peripheral innervation and nociception in reticular type and erosive type of oral lichen planus

Siriporn Chattipakorn1, Jitjiroj Ittichaicharoen1, Samreung Rangdaeng2, Nipon Chattipakorn3,  
1 Department of Oral Biology and Diagnostic Science, Faculty of Dentistry, Chiang Mai University, Chiang Mai, Thailand
2 Department of Pathology, Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand
3 Cardiac Electrophysiology Research and Training Center, Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand

Correspondence Address:
Siriporn Chattipakorn
Department of Oral Biology and Diagnostic Science, Faculty of Dentistry, Chiang Mai University, Chiang Mai


Background: Oral lichen planus (OLP) is a chronic inflammatory lesion in oral mucosa. Reticular (OLP-R) and erosive (OLP-E) types of OLP are the common forms that have been found in dental clinics. The aim of this investigation is to determine the correlation between neurogenic inflammation and nociception associated with OLP-R and OLP-E. Materials and Methods: The oral mucosal lesions from six patients with OLP-E, four with OLP-R and three with noninflamed oral mucosa, which represent normal mucosa, were identified by morphometric analysis of nerve fibers containing immunoreactive protein gene product (PGP) 9.5. The level of inflammation was measured with hematoxylin and eosin staining and the level of nociception was analyzed with visual analog scale measurement. Results: We found that 1) an increase in peripheral innervation was related to the size of the area of inflammatory cell infiltration from both OLP-R and OLP-E; 2) the pattern of PGP 9.5-immunoreactivity among OLP-R and OLP-E was not significantly different (P=0.23); and 3) the correlation between nociception and an increase in PGP 9.5-immunoreactivity was not found in OLP-E and in OLP-R. Conclusions: Our findings suggest that an increase in peripheral innervation may lead to increased inflammation, which is part of the immunopathogenesis of OLP. Differences in nociception between OLP-R and OLP-E arise from the pathogenesis of each lesion, not from the differences in peripheral innervation.

How to cite this article:
Chattipakorn S, Ittichaicharoen J, Rangdaeng S, Chattipakorn N. Changes in peripheral innervation and nociception in reticular type and erosive type of oral lichen planus.Indian J Dent Res 2011;22:678-683

How to cite this URL:
Chattipakorn S, Ittichaicharoen J, Rangdaeng S, Chattipakorn N. Changes in peripheral innervation and nociception in reticular type and erosive type of oral lichen planus. Indian J Dent Res [serial online] 2011 [cited 2023 May 30 ];22:678-683
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Full Text

During the past few years, substantial evidence for a relationship between the immune and the nervous systems has been reported. For example, 1) antigen-presenting dendritic cells or immune cells of the epidermis have been shown to be in close contact with cutaneous nerve fibers [1] and 2) neuropeptides, i.e. mediators released by cutaneous nerves, have been demonstrated to influence antigen-presenting cells or immune cells in skin. [2] There is evidence that changes in the skin innervation observed in dermatological diseases contribute to the inflammatory process and to the associated painful sensation. An increase in cutaneous nerve fibers has been reported in itching and painful cutaneous diseases including neurofibroma, [3] nostalgia paraesthetica, [4] prurigo nodularis, [5] vulvodynia [6] and psoriasis. [7],[8] In contrast, a reduction of cutaneous nerve fibers can be found in conditions associated with decreased cutaneous nociception, such as diabetic neuropathy, [9] leprosy, [10] or HIV-infected patients suffering from xerosis. [11] The current theory of persistent pain following tissue injury or inflammation is that sensitization involves both the central [12],[13],[14],[15] and peripheral nervous systems. [16] A number of studies suggest that the interaction between the inflammation and neural system exists and may lead to painful sensation. [16]

Oral lichen planus (OLP) is a chronic inflammatory disease of the oral mucosa. [17],[18] Clinically, OLP is commonly found bilaterally and may present as striated, plaque, atrophic or erosive lesions. OLP is histologically characterized by a well-defined, band-like lymphocytic subepithelial inflammation. OLP usually presents with burning sensation or persistent pain. Although OLP is classified into six types, the reticular type (OLP-R) and erosive type of OLP (OLP-E) are the two most common types. Each type has different clinical features. OLP-R presents without a painful sensation, whereas pain is the most commonly found symptom in OLP-E. Although it has been shown that cutaneous innervation or peripheral sensitization is increased following chronic inflammation in dermatological diseases [3],[4],[5],[6],[7],[8] and oral lichen planus, [19] information regarding the correlation between neurogenic inflammation and nociception associated with oral mucosal disease such as OLP-R and OLP-E is limited. The present study sought to determine whether 1) two different types of OLP with different levels of nociception, OLP-R and OLP-E, express different patterns of nerve sprouting or peripheral sensitization, and 2) a correlation of an increase of peripheral innervation, inflammatory reaction, and nociception in both OLP lesions exists.

 Materials and Methods

Patient selection

Thirteen patients with oral mucosal lesions were included in this study. None of the patients had a history of either systemic disease or corticosteriod injections to their lesions. All patients had been treated for Candida infection before biopsy. Clinical details of these patients are shown in [Table 1].{Table 1}

All patients were asked to rank the painful sensation of oral lesions before biopsy using a visual analog scale (VAS) system, in which "0" meant no pain at all and "10" meant as painful as imaginable. Biopsies from the oral mucosa of these thirteen patients were obtained. From histological examination, six patients were diagnosed with OLP-E, four with OLP-R and three with noninflamed oral mucosa from the operculum of a third molar after surgical removal of the tooth. The lesions were classified histologically using WHO criteria. [20]

All biopsies came from the buccal mucosa under local anesthesia (2% lidocaine with 1000,000 units norepinephrine). In this study, the biopsy of the OLP-E lesions was performed at the edge of erosive area with the white-striated lesions and the biopsy of the OLP-R lesions was performed at the white-striated area. Some slices of all tissue samples were used for routine histological evaluation including hematoxylin and eosin (H and E) staining. Other slices of all samples were used for protein gene product 9.5 (PGP 9.5) immunohistochemical analysis.

Informed consent was obtained from all patients, and the research plan was accepted by the Ethics Committee of the Faculty of Dentistry, Chiang Mai University, Thailand.


Three-micron thickness paraffined sections were mounted on 3-aminopropyltriethoxysilane (Dako, Glostrup, Denmark)-coated slides. Sections were deparaffinized with xylene and ethanol and then placed in a boiling solution of freshly prepared citrate buffer (pH 6.0) for 10 min in a pressure cooker before immunostaining. Endogenous peroxidase was inhibited by soaking the sections in 0.3% H 2 O 2 in 0.1 M phosphate-buffer saline (PBS) for 30 min at room temperature. The sections were incubated sequentially in a humidified chamber with 1) 3% normal goat serum in 0.1 M PBS (3% NGS, Sigma, St. Louis, MO, USA) as a blocking serum at room temperature for 1 h; 2) primary mouse monoclonal antisera PGP 9.5 (Novacastra Co, Wetzlar, Germany) diluted 1: 20 in 3% normal goat serum overnight at + 4°C; 3) biotinylated goat anti-mouse IgG (Santa Cruz Biotech, Santa Cruz, CA, USA) diluted 1:200 in 0.1 M PBS for 1 h at room temperature; and 4) avidin-biotin-peroxidase complex (Santa Cruz Biotech, Santa Cruz, CA, USA) for 45 min at room temperature. After each step, the sections were rinsed three times in PBS for 5 min. Staining was amplified with the glucose oxidase-3, 3-diaminobenzidine (DAB)-nickel method for 10 min. Sections were washed three times with water for 5 min. The slides were dehydrated in alcohol and xylene, before being mounted in permount (Sigma, St. Louis, MO, USA).

Microscopic evaluation and qualitative assessment

Microscopic examination was performed with an Olympus microscope coupled for morphometric assessment with a digital camera and linked to a semiautomatic Kontron image analysis and processing system. Morphometry of PGP 9.5 immunoreactivity (PGP 9.5-ir) and H and E staining were performed under ×200 magnification. Nerve fiber densities or PGP 9.5-positive fibers (linear intercept number/mm 2 tissue) were performed from the subepithelial area (i.e. an area extending 100 mm deep from the basement membrane area to the lamina propria) in each section as described in a previous study. [19] In each patient, nerve fibers densities were counted in five microscopic fields, in which were covered the whole area in each slide and counted three slides per sample. The epithelium was excluded from the measurement.

Statistical analysis

Results were expressed as the mean ± standard error of the mean (SEM). For comparison between multiple groups, nonparametric analysis with Kruskal-Wallis test and Pearson correlation coefficient were used for data analysis.


Overall innervation as assessed by PGP 9.5-ir as a marker

To determine the pattern of cutaneous innervation of OLP-E, OLP-R and the noninflamed oral mucosa, representing normal mucosa, PGP 9.5-immunoreactivity (PGP 9.5-ir) was used. The specificity of this primary PGP 9.5 antiserum was previously tested in previous studies. [19],[21] An absence of staining was found when the primary antibody was omitted [Figure 1]a, c, e and g. The peripheral nerves visualized by the general neural marker PGP 9.5-ir were easily noticeable. In noninflamed oral mucosa (OM), nerve fibers were located in the deep lamina propria. They were rarely found in close contact with basement membrane. Nerve trunks and rich perivascular innervation appeared in the deeper parts of lamina propria [Figure 1]b, d. However, in both types of OLP, PGP 9.5-positive nerve fibers were concentrated in the superficial subepithelial tissue, and nerve fibers in OLP were found close to the basement membrane [Figure 1]f, h. As shown in [Figure 2], the pattern of PGP 9.5-positive nerve fibers in OLP-R and OLP-E was similar. Means of PGP 9.5-positive never fibers per each subepithelial area of OM (1.0 ± 1.0 linear intercept/mm2 ), OLP-R lesions (2.4 ± 0.8 linear 0.8 linear intercept/mm 2 ) and OLP-E lesions (3.5 ± 1.2 linear intercept/mm 2 ) were not significantly different (P=0.39) [Figure 2]c. Furthermore, PGP 9.5-positive nerve fiber density of both types of OLP lesions was high at the superficial subepithelial areas. Underneath this area, i.e. connective tissue layer, high lymphocytic infiltration was seen where no PGP 9.5-positive fibers were found [Figure 3]a-d. By contrast, neither PGP 9.5-positive nerve fibers nor inflammatory infiltration at the superficial subepithelial areas were found in noninflamed oral mucosa tissue [Figure 3]e, f. Hence, the density of PGP 9.5-positive nerve fibers was greatest in the subepithelial inflamed area of both types of OLP lesions, suggesting the existence of a neuroinflammatory process or peripheral sensitization in this disease as in other inflammatory dermatological diseases. In addition, the pattern of peripheral innervation between the two different clinical features of OLP-R and OLP-E were not different.{Figure 1}{Figure 2}{Figure 3}

No correlation of innervation and pain levels as assessed by means of VAS in OLP-E and OLP-R

To determine whether correlation between peripheral sensitization or nerve sprouting and nociception exists, VAS was used as a pain sensation measurement. VAS and PGP 9.5-positive nerve fiber densities were compared in each patient. We found that the average VAS scores in patients with OLP-E (3.12 ± 1.12, n=6) were significantly greater than those in patients with OLP-R (0 ± 0, n=4, P=0.005). However, a correlation between means of PGP 9.5-positive nerve fiber density and VAS scores existed in patients with OLP-R (r=0.0, P=0) and in patients with OLP-E (r=0.21, P=0.7) was not found [Figure 4]. Although an increase in innervation of OLP-E lesions were similar in quality and quantity to that of OLP-R lesions, the pathophysiological changes of epithelial lesions from both types of lesion were different. Loss of epithelium was the characteristic of OLP-E; in contrast, parakeratinized epithelium was distinct in OLP-R. These data imply that it is the epithelial changes in the lesions, not the number of peripheral nerve fibers, which are related to nociception in OLP lesions.{Figure 4}


Our findings have confirmed the earlier findings that 1) the pattern of innervation in the normal oral mucosa is described as a discontinuous network in the deep lamina propria with no appearance in the superficial lamina propria; [22] 2) the increase in PGP 9.5-positive nerve fibers at the superficial lamina propria was seen in OLP; and 3) the pathophysiological changes in innervation are associated with chronic inflammation. [19] In addition, we have demonstrated that 1) the pattern of innervation in OLP-R and OLP-E is similar, despite the fact that the painful sensations in each is different; and 2) nociception and an increase of nerve sprouting in the superficial lamina propria is not correlated in either OLP-E lesions or in OLP-R lesions.

Nerve sprouting and chronic inflammation in OLP

An increase in PGP 9.5-positive nerve fibers was always observed in both OLP lesions but not in the normal mucosa. These results could be due to both nerve sprouting and collateral formation in OLP lesions. The regeneration of nerve fibers in OLP lesions may occur after tissue injury and may follow angiogenesis of inflamed tissue as demonstrated in previous studies. [23] Sprouting has been demonstrated in other inflammatory models such as: 1) in adjuvant-induced arthritis at the border zone of inflammation [24],[25] and 2) in the wound healing of skin lesions from chronic constrictive injury of sciatic nerves or capsaicin-induced depletion of sensory C-fibers in animal models. [26] The induction factors for the existence or elongation of PGP 9.5-positive nerve fibers in lichen planus may be the local mediators secreted by inflammatory cells as reported in previous studies. [24],[25] It is also possible that the elongation process of PGP 9.5 positive nerve fibers in lichen planus may act as an attempt at regeneration after chronic inflammation.

The pattern of sprouting from OLP-R and OLP-E was seen to follow the pattern of lymphocytic inflammation. In OLP lesions, the band-like lymphocytic inflammation was found in the subepithelial layers or superficial lamina propria, and the nerve sprouting was also restricted to the superficial lamina propria. This finding suggests the existence of the reaction between neurogenic and immune systems. In addition, our findings support the theory of neurogenic inflammation in chronic inflammatory diseases. [18],[23],[27]

Increased peripheral innervation and nociception in OLP

PGP 9.5-immunoreactivity (PGP 9.5-ir) was used to locate single nerve fibers, nerve bundles, and nerves surrounding vessels and innervating muscles and glands. [21] Although PGP 9.5-ir reflects the general innervation pattern of the tissue, several studies have shown that PGP 9.5-positive nerve fibers were correlated with nociception. For example, 1) the increase of PGP 9.5-positive nerve fibers at skin lesions was found with an increase in painful sensation such as thermal hyperalgesia and mechanical allodynia in a chronic constrictive injury in an animal model of painful partial nerve injury; [28],[29] 2) loss of cutaneous pain sensation with a reduction of PGP 9.5-positive nerve fibers in leprosy skin lesions [30] and 3) PGP 9.5-positive nerve fibers were reduced in the capsaicin-induced dermal lesion in a rat model, in which capsaicin induces depletion of sensory C-fiber neuropeptides. [26] All of the findings from these previous reports suggest that PGP 9.5 positive nerve fibers are very well correlated with nociceptors. In this study, we found that the mean number of PGP 9.5-positive nerve fibers was not correlated with nociception in OLP-E or in OLP-R. The difference in nociception in both OLP types may be the result of pathophysiological changes in both types of lesion. OLP-E is characterized by loss of mucosal epithelium, which leads to the exposure of lamina propria to the surrounding environment in the oral cavity. OLP-R, however, has parakeratinized epithelium covering the mucosal lesion. Although the pattern and number of PGP 9.5-positive nerve fibers from both lesions are not significantly different, the pathophysiological nature of epithelium from both lesions is totally distinguishable. The epithelial differences in the pathophysiology of OLP-R and OLP-E may be the reason for the difference in pain sensation, because sensory afferents may receive stronger and/or more frequent nociceptive input in OLP-E than in OLP-R. The reason that being no difference in lymphocytic infiltration or PGP 9.5-positive nerve fibers were seen between OLP-E and OLP-R could be due to the fact that extensive lymphocytic inflammation could lead to the loss of nerve fibers in that area, as seen in previous study. [19]

Limitation of this study

Although the pattern of sprouting in OLP lesions in our study was similar to the pattern in a previous study, [19] the number of PGP 9.5-positive nerve fibers was much less than in the previous report. [19] This difference may be due to different techniques used in each study. We used paraffined sections with pressure-cooking techniques as antigen-unmasking techniques, whereas the previous study used frozen sections without antigen-unmasking. Our technique could have led to the loss of some tissue during the immunochemical process.


Chronic subepithelial inflammation is a diagnostic feature of OLP. Although OLP-E and OLP-R have similar inflammatory responses, the nociception or stressful sensations in patients with the respective OLP lesions are different. The present work suggests that the difference in nociception between both OLP lesion types relates to the structural changes in the epithelium rather than the increase of nerve sprouting from the lesions. In addition, this study supports the relationship between associated neurogenic factors and inflammatory processes in OLP lesions.


The authors thank Drs. S. Pongsiriwet and S. Krisanaprakornkit for their support in the Oral Medicine Clinic, R. Kitikamdhorn for the technical support, and Professor M. Kevin O Carroll, Professor Emeritus, University of Mississippi School of Dentistry and Faculty Consultant, Faculty of Dentistry, Chiang Mai University, for his editorial assistance during manuscript preparation. This study was supported by the Internal Research Fund of Chiang Mai University (SC) and a grant from the Thailand Research Fund to SC (BRG5480003) and to NC (RTA 5280006).


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