papillary thyroid carcinoma ( ptc ) is usually an indolent disease showing an excellent prognosis if competently resected . however , it is also well known that ptc can recur to various organs after surgery . the organ to which ptc will most likely recur is the regional lymph node , and such recurrence is not immediately life threatening with a few exceptions .   however , ptc can also recur in distant organs such as the lung , bone , and brain . although distant recurrence is less frequent , it can be fatal if recurrent lesions are progressive and refractory to radioactive iodine ( rai ) therapy . subcutaneous or intrastrap muscular ( sim ) recurrence is a rare site for ptc recurrence . the most common cause of sim recurrence is needle tract implantation during fine needle aspiration biopsy ( fnab ) for the diagnosis of ptc . we previously showed that needle tract implantation occurred in 0.14% of patients who underwent fnab for ptc . other potential etiologies of sim recurrence are attachment and proliferation of carcinoma cells transported in the bloodstream to subcutaneous tissue or intrastrap muscle , lymphatic metastasis to subcutaneous lymph node , and intraoperative dissemination of carcinoma cells . little is known about the clinical significance of sim recurrence possibly because of its rarity . to date , we encountered 29 patients with ptc who showed sim recurrence , and in this study , we investigated the impact of this event on the clinical course of ptc patients . these patients underwent fine needle aspiration biopsy ( fnab ) before surgery and were diagnosed as having ptc . after surgery , surveillance for local recurrence was performed at least once per year by ultrasonography .   to date , 29 patients ( 0.29% ) all these lesions were diagnosed as ptc recurrence on fnab or thyroglobulin measurement of the washout of needles .   similarly , 3 patients who underwent initial surgery at other hospitals , and then received postoperative followup in our hospital showed sim recurrence . they consisted of 24 females and 5 males , and patient ages at the initial surgery ranged from 30 to 79 years ( average 61 years ) . the extent of thyroidectomy at initial surgery was total thyroidectomy in 14 patients and limited thyroidectomy in the remaining 15 patients . the extent of lymph node dissection included both the central and lateral compartments in 24 patients and only central node dissection in 2 patients . patients who showed other accompanying thyroid malignancies in the primary lesions or in lymph node metastases such as anaplastic carcinoma , poorly differentiated carcinoma on who classification or turin proposal [ 4 , 5 ] , follicular carcinoma , medullary carcinoma , and malignant lymphoma were excluded from the series . patients whose regional lymph node metastasis directly invaded the subcutaneous tissue and whose other recurrent lesions were diagnosed as anaplastic carcinoma before the detection of sim recurrence were also excluded . to date , 28 of 29 patients underwent surgical dissection of recurrent lesions that were diagnosed as ptc on pathological examination . the intervals between initial surgery and appearance of sim recurrence ranged from 10 to 172 months , and the average interval was 79 months . distant recurrence was evaluated on chest ct scan , roentgenography , or pet - ct scan . the entire follow - up period from initial surgery ranged from 28 to 234 months ( average 137 months ) . to date , 29 patients with ptc showed sim recurrence .   backgrounds and preoperative clinical features of these patients at initial surgery are summarized in table 1 . twenty - four patients ( 83% ) were aged 55 years or older at the initial surgery , and 20 ( 76% ) had primary lesions larger than 2  cm . twelve patients ( 46% ) were classified as n1a or n1b on the uicc tnm classification , because they showed lymph node metastasis detectable on preoperative imaging studies , and 4 ( 15% ) had node metastasis measuring 3  cm or larger . ten patients ( 38% ) were classified as stage iva , while only 4 ( 15% ) were classified as stage i.   
 table 2 indicates intraoperative and pathological findings at initial surgery for these 29 patients . extrathyroid extension corresponding to t4 on tnm classification   was detected in 9 patients ( 35% ) . similarly , node metastasis of 3 patients ( 12% ) extended to adjacent organs requiring at least partial resection of these organs .   on pathological examination , lymph node metastasis was detected in 24 patients ( 92% ) , and 20 ( 77% ) were graded as pstage iva . all but one patient , who rejected further therapy , underwent surgery for sim recurrence , and all were pathologically diagnosed as having ptc . subcutaneous or intrastrap muscular tissue was the first organ showing ptc recurrence in 19 patients ( 66% ) , and 12 ( 41% ) have shown no further recurrence to date . four of these 5 patients showed recurrence twice , and the remaining one showed recurrence three times . two patients underwent external beam radiotherapy to the neck after surgical dissection of sim recurrence . one of these patients has shown no further recurrence to the neck to date , but another showed further sim recurrence even after external beam radiotherapy . seventeen patients ( 59% ) , including the remaining 7 ( 19 minus 12 ) , showed recurrence to other organs . fifteen patients ( 52% ) showed local recurrence , and 13 ( 45% ) showed distant recurrence . local organs to which ptc recurred were the lymph node in 13 patients and the remnant thyroid in 2 patients . distant organs showing recurrence were the lung in 11 patients , bone in 2 patients , and brain in 1 patient . of 13 patients showing distant recurrence , only 1 showed sim recurrence after distant recurrence . the remaining 8 showed distant recurrence after the detection of sim recurrence , and the intervals between these recurrences ranged from 10 to 77 months . to date , 3 of 13 patients who showed distant recurrences have died of ptc 17 , 52 , and 69 months after the detection of sim recurrence , respectively ( table 3 ) . two patients showed preoperatively detectable node metastasis , and the primary lesions in two patients showed extrathyroid extension . none of the patients in our series died of uncontrollable growth , including anaplastic transformation , of sim recurrence . table 4 summarizes the relationship between distant recurrence and clinicopathological features of 29 patients with sim recurrence . patients showing clinical node metastasis were significantly more likely to show distant recurrence than those without clinical node metastasis . especially , all 3 patients who had extranodal tumor extension showed distant recurrence after the detection of sim recurrence . although there was no significant difference , patients with extrathyroid extension tended to show distant recurrence more frequently than those without extrathyroid extension . in this study , we reviewed the records of patients with sim recurrence in order to elucidate the clinical significance of this rare event . we previously showed that age 55 years or older , clinical node metastasis ( especially large node metastasis ) , extrathyroid extension , and extranodal tumor extension were important signs of biological aggressiveness of ptc [ 1 , 7 ] .   in the series of patients with sim recurrence , the incidences of patients aged 55 years or older , clinical node metastasis , node metastasis larger than 3  cm , extrathyroid extension , and extranodal tumor extension were 83% , 46% , 15% , 35% and 12% , respectively . we analyzed 5911 patients with ptc who underwent surgery between 1987 and 2006 , and these incidences in this series were much lower at 40% , 20% , 3% , 13% , and 2% , respectively . it is therefore suggested that sim recurrence is likely to occur in ptc patients displaying high - risk features . we have to note that 13 patients in our series also had distant recurrence , accounting for as much as 45% . all patients except one showed distant recurrence after or at the same time as detection of sim recurrence . these findings strongly suggest that sim recurrence is a strong predictor of distant recurrence . this is possibly because ptc showing such an unusual lesion , whatever its mechanism , shows high metastatic activity and proliferating activity in metastatic lesions . it is also noteworthy that 66% of patients showed sim recurrence as the initial sign of recurrence . therefore , when we encounter sim recurrence , an immediate search for other metastases is recommended . even when no other recurrences could be detected , these patients should thereafter undergo more careful followup than previously . we also showed that patients with high - risk features such as advanced age , extrathyroid extension , and clinical node metastasis were more likely to show distant recurrence . therefore , we must prepare for a high incidence of distant recurrence , especially in patients with high - risk features , when sim recurrence is detected .       to date , 3 patients have died of ptc but none of these died of sim recurrence , indicating that sim recurrence is generally not fatal at least in our series . this may be because all patients except one underwent surgery immediately after the detection of sim recurrence . one patient did not develop further recurrence thereafter , but the other showed further recurrence .   therefore , it remains unknown whether external beam radiotherapy is effective for sim recurrence , but it may be a therapy option after surgical dissection . for patients whose sim recurrence is detected as an initial recurrence of ptc and other recurrent lesions were simultaneously detected , surgery should be performed not only for sim recurrence but also for other lesions . furthermore , if patients underwent limited thyroidectomy at the initial surgery , completion total thyroidectomy should be performed because such patients will show high incidences of distant recurrence requiring rai therapy , and followup of thyroglobulin level will not be necessary .       in summary , however , sim recurrence is a predictor of distant recurrence especially for patients with high - risk factors , regardless of the mechanism underlying sim recurrence . careful investigation of other recurrences at the time sim recurrence is detected and careful followup after surgical dissection are highly necessary for such patients .
subcutaneous or intrastrap muscular ( sim ) recurrence is rare in papillary thyroid carcinoma ( ptc ) patients , and its clinical significance remains unclear . 
 we analyzed 29 patients with ptc who showed sim recurrence in order to elucidate this issue . 
 the incidence of patient age 55 years or older at initial surgery , extrathyroid extension , and clinically detected lymph node metastasis was 83% , 35% , and 46% , respectively . 
 after surgical dissection , 17% of patients showed repeated sim recurrence . 
 distant recurrence was detected in 45% of patients and was more likely to occur in patients with high - risk clinicopathological features . in all but one patient in this series 
 , distant recurrence was detected at the same time or after the detection of sim recurrence . 
 three patients died of ptc , but none of these patients died of the development of recurrent sim lesions . 
 these findings suggest that although sim recurrence is a rare event and is not fatal , it is a predictor of distant recurrence especially in patients with high - risk clinicopathological features . 
 careful followup is recommended for such patients .