Isolated skeletal muscle metastatic deposit in a patient with micropapillary carcinoma thyroid identified by 18F FDG PET CT

Abstract

Micropapillary carcinoma of thyroid is said to be low risk differentiated thyroid malignancy with excellent prognosis. We report the identification of an isolated FDG avid muscle deposit in a treated case of micropapillary carcinoma of the right lobe and widely invasive follicular carcinoma of the left lobe thyroid gland. Patient was found to have an elevated thyroglobulin level with negative iodine scan (TENIS syndrome) on follow up at 6 months. An 18F FDG PET CT (18 fluorine-fluorodeoxyglucose positron emission computed tomography) whole body study revealed a solitary FDG avid deltoid muscle deposit which was histopathologically confirmed to be metastatic papillary carcinoma. While follicular carcinoma is known to have distant metastases, this may be the first reported case of solitary skeletal metastases from micropapillary carcinoma of thyroid and probably the second reported skeletal muscle deposit from DTC detected on 18F FDG PET CT done following elevated thyroglobulin level and negative 131 iodine WB scan (TENIS). This case also assumes importance because it demonstrates possibility of metastases even from a micropapillary carcinoma in contrast to American Thyroid Association guidelines (2009) which suggests that micropapillary carcinoma of thyroid does not merit further treatment after a Total Thyroidectomy.

Skeletal Muscle Metastasis in Papillary Thyroid Microcarcinoma Evaluated by F18-FDG PET/CT

“…A case of PTC presenting as a solitary metastasis in the right arm muscle in an elderly hyperthyroid male patient was mentioned by Pucci et al [18]. Similar to our study, the only case of papillary microcarcinoma skeletal metastasis found in the literature, is presented by Sarma et al, considering a 66 years old male left deltoid metastasis found on an FDG-PET/CT scan, after negative 131-iodine WBS while thyroglobulin level was 123.2 ng/mL [7]. Zhao et al reported the case of rectus abdominis muscle metastasis from PTC identified by I-131 SPECT/CT as an incidental focus of abnormally increased I-131 uptake [20].…”

“…The most common skeletal metastasis site appears to be the erector spinae [14][15][16]19] and thigh muscle group [10][11][12][13]. Unique cases of muscle metastasis sites were reported localized in trapezoid [17], arm biceps [18], deltoid [7], gastrocnemius [9], and rectus abdominis [20] muscles. In summary, to the best of our knowledge, this is the second reported case of distant solitary skeletal metastasis from papillary thyroid microcarcinoma.…”

“…Usually papillary microcarcinoma has an excellent prognosis [6]. To our knowledge, there has been only one report in the specialty literature of muscular metastasis from papillary microcarcinoma [7]. A unique case of metastatic thyroid papillary microcarcinoma to the gluteal muscle is presented, including a review of all thirteen cases reported in the literature.…”

Skeletal muscle metastases from papillary and follicular thyroid carcinomas: An extensive review of the literature

“…The most common muscle involved in PTC/FTC malignancy was the gluteus muscle, as observed in 16% of reported cases, compared with the erector spinae muscles as concluded by other modern papers ( 8 , 10 , 17 ). The present review of the literature identified just 4 cases of erector spinae DTC metastasis (7%).…”

“…In 2015, Portela et al ( 16 ) presented a case of PTC muscle metastasis within the sternocleidomastoid muscle and reviewed the literature, identifying just 1 previous case of PTC muscle metastasis. Sarma et al ( 17 ) described a case of FTC deltoid muscle metastasis; from reviewing the literature, the authors reported just 3 cases of solitary DTC muscle metastases. Cassidy et al ( 18 ) reported a case of PTC muscle metastasis; they reported 3 documented cases of symptomatic PTC muscle metastasis, and 3 cases of incidentally diagnosed PTC by single-photon emission computed tomography/CT and PET/CT, from the literature.…”