Thyroid Research and Practice

CASE REPORT
Year
: 2017  |  Volume : 14  |  Issue : 2  |  Page : 77--80

Distant skeletal muscle metastasis to sternocleidomastoid in the setting of recurrent papillary thyroid carcinoma


Nitish Virmani, Jyoti Dabholkar 
 Department of Otorhinolaryngology and Head-Neck Surgery, Seth G.S. Medical College and KEM Hospital, Mumbai, Maharashtra, India

Correspondence Address:
Nitish Virmani
H. No. 576, Sector 37, Faridabad - 121 003, Haryana
India

Abstract

Papillary thyroid carcinoma (PTC), the most common form of differentiated thyroid cancer, is characterized by an indolent course and excellent prognosis. Although its spread to regional lymph nodes is well known, distant metastases are seen only in a minority of patients with lungs being the most common site. Skeletal muscle metastases are extremely rare even in follicular thyroid carcinoma, in which hematogenous spread is known to occur. We describe a case of skeletal muscle metastasis to sternocleidomastoid muscle in a case of PTC in the setting of local recurrence.



How to cite this article:
Virmani N, Dabholkar J. Distant skeletal muscle metastasis to sternocleidomastoid in the setting of recurrent papillary thyroid carcinoma.Thyroid Res Pract 2017;14:77-80


How to cite this URL:
Virmani N, Dabholkar J. Distant skeletal muscle metastasis to sternocleidomastoid in the setting of recurrent papillary thyroid carcinoma. Thyroid Res Pract [serial online] 2017 [cited 2021 Dec 3 ];14:77-80
Available from: https://www.thetrp.net/text.asp?2017/14/2/77/207134


Full Text



 Introduction



Differentiated thyroid cancers (DTCs) are generally characterized by an indolent progression and a 10-year survival rate as high as 80%–95%.[1] They usually remain localized to the gland. Distant metastases are seen only in a minority of patients, the most common sites being lungs followed by mediastinal lymph nodes and bone. Rarely, they have been reported to involve brain, breast, liver, kidney, and skin. Skeletal muscle metastases are extremely uncommon in DTC, and only a few cases have been reported in literature. We describe a case of recurrent papillary thyroid carcinoma (PTC) with a focal metastatic deposit within the sternocleidomastoid muscle.

 Case Report



A 45-year-old woman had undergone total thyroidectomy at a peripheral center in 2010. Unfortunately, no surgical records were available for review. She had stopped taking thyroxine supplements around 2 years ago. In 2015, she presented to us with progressively increasing neck swelling for 1 year. Physical examination revealed 8 cm × 7 cm soft, cystic, nontender swelling in the anterior neck extending between anterior borders of either sternocleidomastoid muscle. Overlying skin was fixed to the underlying tumor. There was an overlying healthy scar. There was no clinical evidence of retrosternal extension. A 2 cm × 2 cm hard, nontender, and mobile swelling was palpable over the right sternocleidomastoid muscle at the level of hyoid bone [Figure 1].{Figure 1}

Fine needle aspiration cytology from anterior swelling was reported as malignant thyroid lesion, which could not be typed, and that from lateral swelling was suggestive of metastasis from PTC. Computed tomography (CT) scan was done to ascertain the extent of local recurrence. The lateral swelling was visualized as an intensely enhancing nodule with scattered foci of necrosis, entirely within the right sternocleidomastoid muscle, suggestive of intramuscular metastatic deposit [Figure 2]. Positron emission tomography (PET)-CT was done to ascertain distant metastasis in the setting of recurrent disease [Figure 3].{Figure 2}{Figure 3}

Her thyroid function tests (T3 <20 ng/dl; T4 <0.47 μg/dl; thyroid-stimulating hormone (TSH) >60 μIU/ml) were suggestive of severe hypothyroidism. We started her on 200 μg/day of oral levothyroxine for 2 days followed by 100 μg/day. Her TSH levels normalized in 2 weeks (4.17 μIU/ml). Subsequently, she underwent wide excision of local recurrence (including involved skin) and bilateral central and lateral compartment neck dissection. The intramuscular metastatic deposit was identified within the upper third of sternocleidomastoid muscle. This portion of muscle was excised [Figure 4]. Final histopathology was suggestive of PTC with metastasis to sternocleidomastoid. Five metastatic nodes were identified. She was referred for adjuvant radioiodine therapy but unfortunately was lost to follow-up thereafter.{Figure 4}

 Discussion



The risk of distant metastases is greater in follicular thyroid carcinoma because of its tendency to spread through hematogenous route. PTC, however, typically disseminates to regional lymph nodes. Distant metastases from PTC occur with a frequency ranging from 1.73% to 8.4% in most studies.[2] The most common site is lung followed by mediastinal lymph nodes and bone.[3] Rarely, metastatic disease can involve liver, brain, breast, kidney, ovaries, and skin.

Hematogenous metastasis to muscle is extremely rare even though it forms >40% of total body weight. A probable hypothesis is that skeletal muscle is a hostile environment for retention and proliferation of cancer cells, including muscle motion, unadapted muscle pH, and muscle's ability to remove tumor-produced lactic acid.[4]

It is difficult to ascertain the exact incidence of skeletal muscle metastasis in DTC; only a few isolated case reports exist in literature. Metastatic deposits have been found in erector spinae, vastus medialis, gluteus maximus, gluteus medius, biceps, and rectus abdominis muscle.[5],[6],[7],[8],[9],[10] Most of these have been associated with distant metastasis to other sites although isolated muscle deposits have also been reported. There were coexistent pulmonary metastatic deposits in our case.

Iodine-131 whole-body scan is a sensitive test to evaluate DTC patients for possible metastatic disease. However, clinicians should be aware that false-negative radioactive iodine scans are seen in up to 20% of patients with original well-DTCs.[11] The role of fluorodeoxyglucose (FDG) PET/CT in identifying disease in such patients is well known. FDG PET/CT also plays an indispensable role in evaluating patients with recurrent neck disease which was the case in our patient. In the presence of iodine-avid residual or recurrent thyroid lesion in the neck, iodine-131 whole-body scan would be unable to pick up distant metastatic disease, thereby necessitating an FDG-PET scan. Moreover, iodine scintigraphy may fail to localize the metastatic foci because of its lack of anatomic detail. PET/CT, single-photon emission CT, and magnetic resonance imaging (MRI) allow for better and accurate localization.[10]

To the best of our knowledge, this is the first case of sternocleidomastoid metastasis reported in literature. One may expect this muscle to be involved by contiguity, either from adjacent thyroid tumor or from underlying metastatic nodes. Even clinically, a swelling palpable in this region would generally be considered a lymph node swelling. However, CT scan correctly identified this swelling to be completely intramuscular. This was further confirmed by intramuscular avid uptake of 18 FDG on PET/CT scanning. There have been reports of involvement of sternocleidomastoid muscle by needle track seeding from fine needle aspiration biopsy [12] and ectopic seeding, following transaxillary robotic thyroid surgery.[13] This possibility does exist in our case too since spillage could have occurred in the first surgery, the details of which are not available with us. However, the presence of isolated cancerous deposit completely within the muscle makes distant metastasis a more likely possibility.

The presence of distant metastases is the most significant poor prognostic factor for survival, with only 50% of metastatic patients surviving after 10 years.[14] An important factor in our patient was TSH levels. She had severe hypothyroidism with grossly elevated TSH levels. TSH being a growth factor for thyroid cells, any increase in TSH level may stimulate cancer growth.

Most of the reported cases of muscle metastasis have been treated by radical excision and radioiodine therapy.[6],[9],[10] External beam radiotherapy has been used for unresectable muscle metastatic deposits.[8] We excised the upper thirds of muscle containing the metastatic deposit during excision of the local recurrence as both were accessible through the same incision. Unfortunately, our patient was lost to follow-up after we referred her for radioiodine therapy.

Lung and bone, being common sites of distant metastasis, usually draw significant concern by clinicians. Rare sites, however, may be missed in the clinical setting. Recognizing patterns of these rare metastases has a significant impact on clinical decision-making and ascertaining prognosis.

 Conclusion



Even though skeletal muscle metastasis is an extremely rare manifestation of PTC, one should be aware of the possibility during postthyroidectomy follow-up of patients, especially in elderly and those with aggressive primary tumors. CT, MRI, and PET allow for superior localization of intramuscular metastatic deposits. Radical surgical excision and radioiodine therapy remain the cornerstone of management.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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