Evidence of Innervation in Talc-Induced Pleural Adhesions: Conclusion

Likewise, it has been reported that the growth of nerve fibers into peritoneal adhesions is dependent on the underlying disease. Thus, it has been shown that peritoneal adhesions from patients with malignant diseases are more likely to contain nerves than adhesions due to other conditions, including inflammatory and noninflammatory diseases.
In all adhesions examined here, nerve fibers appeared to originate from the parietal pleura, which is mainly innervated by the internal intercostal nerves (costal pleura and peripheral part of the diaphragmatic pleura) and the phrenic nerves (central portion of the diaphragmatic pleura and mediastinal pleu-ra). A recent electrophysiologic and pharmacologic study reported that the parietal pleural afferents were myelinated A8 and unmyelinated C-type nerve fibers. In this regard, the morphologic and ultra-structural characteristics of the nerve fibers here described, including the degree of myelinization (low) and axon diameter (1 to 6 ^m), are totally comparable to those of A8 fibers. Although the effect of innervation on adhesion function is unknown, it is interesting to note that A8 fibers are pain-conducting fibers.
The possible implication of this finding in clinical practice is unknown. In the aforementioned stud-ies on innervation of human peritoneal adhesions, the relationship between innervation and pain reported by the patients was unclear. An interesting question is whether human pleural adhesions may be innervated and, consequently, be a source of chronic pain. Although we have been unable to find any specific report on this issue, in our experience some patients with pleural diseases in which adhesions occur, such as tuberculosis or empyema, report chronic pain in their evolution. In the case of pleurodesis, pain is a frequent short-term adverse effect after pleurodesis with several agents, probably due to the inflammation created in the pleural space. Chronic pain, however, has scarcely been reported; it was described in up to 31% of patients undergoing videothoracoscopic treatment with pleural abrasion for primary or secondary spontaneous pneumothorax,’ although in these cases it is difficult to know whether the pain was due to pleurode-sis itself or to surgery. Regarding talc pleurodesis, to our knowledge two cases of chronic pleuritic pain have been reported. However, the real incidence of chronic pain after talc pleurodesis may have been underestimated, since few studies have assessed the long-term outcome of these patients and chronic pain has never been prospectively evaluated.
With respect to the neovascularization process, our results showed the vascular growth patterns associated with pleural adhesion development to be similar to those described in inflammatory and malignant conditions. Indeed, sprouting and nonsprouting angiogenesis by intussusception were observed in the newly formed vessels and, at 1 week after instillation, all adhesions examined were well vascularized and contained arterioles, capillaries, venules, and lymphatics.

This entry was posted in Pulmonary Function and tagged adhesion, innervation, lymphangiogenesis, neovascularization, pleurodesis, talc, ultrastructure.