Solitary Metacarpophalangeal Metastasis from Poorly Differentiated Thyroid Carcinoma: Excellent Tumor Marker and Scan Response to Two Fractions of Radioiodine Therapy

A 77-year-old-female initially presented with left thumb swelling [Figure 1], which on fine-needle aspiration cytology was found to be metastatic follicular carcinoma of thyroid. X-ray left thumb demonstrated destructive lesion involving the proximal phalanx of thumb with disorganization of metacarpophalangeal joint with soft tissue [Figure 2]. This was consistent with a metastatic deposit. The ultrasonography of the neck showed well-defined hypoechoic mass (3.7 cm × 2.9 cm × 2.2 cm in dimension) in the right lobe of thyroid with peripheral calcification. The patient underwent total thyroidectomy with right central compartment clearance. The final histopathology turned out to be poorly differentiated carcinoma of the right lobe of thyroid, with reactive regional nodes and no extrathyroidal extension. The patient was subsequently treated twice with radioactive iodine (¹³¹I), with excellent clinical, tumor marker, and scan response to administered therapy [Figures 3–5]. The stimulated serum thyroglobulin (Tg) at the time of the 3^rd follow-up was 0.01 ng/ml with no abnormal focus in the scan. Apart from the rare site of metastasis from differentiated thyroid cancer, the case also illustrates the fact that small volume metastatic skeletal disease at times can demonstrate an excellent response to ¹³¹I therapy.[12345]

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Figure 1 The 77-year-old female presented with left thumb swelling: X-ray left thumb demonstrating destructive lesion involving the proximal phalanx of thumb with disorganization of metacarpophalangeal joint. This is consistent with a metastatic deposit. A soft-tissue lesion is also seen in this region

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Figure 2 The 77-year-old female presented with left thumb swelling: X-ray left thumb demonstrating destructive lesion involving the proximal phalanx of thumb with disorganization of metacarpophalangeal joint. This is consistent with a metastatic deposit. A soft-tissue lesion is also seen in this region

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Figure 3 Baseline diagnostic ¹³¹I scan showed iodine avid focus in the left thumb (arrow) with ¹³¹I neck uptake −0.98% (24 h). The baseline serum thyroglobulin (Tg) was >300 ng/ml. The patient was subsequently treated twice with radioactive iodine (¹³¹I) with cumulative dose of 471 mCi

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Figure 4 The first and second ¹³¹I posttherapy whole body scans showed abnormal focal uptake corresponding to the left metacarpophalangeal joint with gradual reduction of uptake with each treatment. The serum thyroglobulin level during the 1^st follow-up reduced to 1.27 ng/ml

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Figure 5 The diagnostic ¹³¹I scan (after 2^nd cycle of radioactive iodine therapy), whole body and static view, showed no abnormal iodine avid focus noted anywhere in the study and serum thyroglobulin at this time was 0.01 ng/ml

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