Post-radiation sciatic neuropathy: a case report and review of the ...

World Journal of Surgical Oncology 2008, 6:130http://www.wjso.com/content/6/1/130DiscussionPathophysiology and clinical courseVery little is known about the pathophysiology and thehistopathological changes that occur in peripheral nervesafter therapeutic irradiation. Early experimental studiesindicated that the peripheral nerves are extremely radioresistant.However, the follow up time was short and it islikely that the injury did not have an opportunity todevelop [3].Today we know that post-irradiation neuropathy occursboth directly and indirectly: directly by the harmful effectof the radiation on the nerve itself, and indirectly by thefibrosis that radiation causes in the tissue around thenerve [2].Direct effects of irradiation on nerve include bioelectricalalterations (subnormal action potentials, altered conductiontime), enzyme changes, abnormal microtubuleassembly, altered vascular permeability and neurilemmaldamage. All of these changes are observed experimentallywithin 2 days after irradiation and are all dose dependentand irreversible [4-6].The secondary damage to the nerve is due to the extensivefibrosis of the connective tissue around the nerve, whichbecomes densely hyalinised. There is also a progressiveloss of elasticity and the development of contractures thatultimately consolidate the adjacent structures with thenerve. In addition, the decreased vascularity of the areamay destroy some adjacent peripheral nerves. Regenerationof the affected nerves may be impeded [2]. In a reportof findings at autopsy in two patients who had post-irradiationbrachial-plexus syndrome [7], varying degrees offibrosis of the neurilemma, as well as demyelinizationand fibrous replacement of the fibrils, were described.Mendes et al. in histological examination of femoral nervebranches removed during surgical decompression of thefemoral nerve, in a patient with post-irradiation femoralneuropathy, also found demyelinated nerve fibres surroundedby abundant scar tissue with areas of hyalinization[2].Peripheral nerve damage is a rare but understandablymajor complication of radiation therapy associated withsignificant morbidity. The frequency of injury reportedfrom some of the older studies is probably higher thanwould occur today as prior to the advent of CT and MRI,larger fields were used because of greater uncertaintyabout the dimensions of the tumour.In studies looking into post-irradiation neuropathyinvolving the brachial and cervical plexuses after radiotherapyfor breast carcinoma it was found that symptomsgenerally begin within one to two years after treatmentand are initially mainly sensory (e.g. burning pain, numbness,paresthesia) [7,8]. Any motor deficits that developare usually delayed for about eighteen months andinclude paresis of a group of muscles and complete paralysisof the arm [9]. Stoll et al. and Powell et al. have bothfound a direct relationship between the dosage of radiationand the severity/time of appearance of symptoms[7,10].In a review of radiation injury to peripheral nerves publishedby Giese and Kinsella the authors conclude thatperipheral neuropathy is relatively infrequent at lowerdoses per fraction [11]. They expressed concern that cofactorssuch as radiosensitizers, chemotherapeutic agentsand surgical manipulations could possibly increase theincidence. Breast cancer patients receiving cytotoxic chemotherapyhad a higher incidence of radiation induced brachialplexopathy compared to those having radiation onlyfollowing mastectomy [12].Any peripheral nerve may be affected by post-radiationneuropathy and it is likely that the unique location of thistumour reflects 1) the special site of radiation therapy and2) the repeated doses of radiation administered [12].Latency is an important factor to be considered when evaluatingnerve injury [12]. Stoll and Andrews did notobserve any neuropathy occurring before 5 months, witha majority occurring between 10 and 22 months after irradiation.They also noted that the higher dose group didshow signs earlier than the lower dose group. Powell et al.did not observe any nerve injury prior to 10 months postirradiation,whereas reports exist in the literature of neuropathiesoccurring as late as 11 years after irradiation forbreast cancer. Therefore, latency, as our case demonstrates,is a very important factor to be considered, sinceshort follow-up times may underestimate the true incidenceof post-irradiation injury to peripheral nerves.ManagementWhen considering management of post-irradiationperipheral neuropathy, it is important to realise that anunalterable condition is the status of the patient's underlyingmalignancy prior to initiation of treatment, includingtumour size, location and structures involved/destroyed [12]. Furthermore, release of entrapped nervesfrom a fibrous mass can be challenging even for the mostskilled surgeon. Therefore, a short life expectancy coupledwith uncertainty of recovery from surgical interventionmake conservative management more appropriate.Also important in overall response to and recovery fromtherapy is the general health of the patient and, if a child,the stage of development and growth [12]. If surgery is apart of the overall treatment, as was in our case, then thePage 4 of 5(page number not for citation purposes)