1-23I-MIBG thyroid uptake: Implications for MIBG imaging of the heart

Thyroid [123I]MIBG uptake in Parkinson’s disease and diabetes mellitus

Thyroid [¹²³I]MIBG uptake is proposed as a tool for differentiating between Parkinson's disease (PD) and diabetes mellitus (DM) on [¹²³I]MIBG scintigraphies since both patient groups show decreased cardiac uptake. One study compared thyroid [¹²³I]MIBG uptake in DM and PD patients and reported reduced [¹²³I]MIBG uptake only in the PD group. Here, we investigated thyroid [¹²³I]MIBG uptake in patients with PD and DM and found severely reduced thyroid [¹²³I]MIBG uptake in DM. Larger studies are needed to substantiate whether DM patients are more or less likely to exhibit decreased thyroid MIBG uptake compared to controls and PD patients.

Systemic Metabolic Alteration Dependent on the Thyroid-Liver Axis in Early PD

OBJECTIVE

Parkinson's disease (PD) is a common neurodegenerative disease characterized by initial involvement of the olfactory bulb/amygdala or autonomic nerves followed by nigral degeneration. Although autonomic innervation strictly regulates multiorgan systems, including endocrine functions, circulation, and digestion, how dysautonomia in PD affects systemic metabolism has not been identified. In this study, we tried to estimate the pathogenic linkage of PD by nuclear medicine techniques, trans-omic analysis of blood samples, and cultured cell experiments.

METHODS

Thyroid mediastinum ratio of ¹²³ I-metaiodobenzylguanidine (MIBG) scintigraphy was measured in 1,158 patients with PD. Furthermore, serum exosome miRNA transcriptome analysis and plasma metabolome analysis followed by trans-omic analysis were performed in patients with de novo PD and age-matched healthy control persons. Additionally, thyroid hormone was administered to skeletal muscle and liver derived cells to evaluate the effect of hypothyroidism for these organs.

RESULTS

Sympathetic denervation of thyroid correlating with its cardiac denervation was confirmed in 1,158 patients with PD by MIBG scintigraphy. Among patients with drug-naïve PD, comprehensive metabolome analysis revealed decreased levels of thyroxine and insufficient fatty acid β-oxidation, which positively correlate with one another. Likewise, both plasma metabolome data and transcriptome data of circulating exosomal miRNAs, revealed specific enrichment of the peroxisome proliferator-activated receptor (PPARα) axis. Finally, association of thyroid hormone with PPARα-dependent β-oxidation regulation was confirmed by in vitro experiments.

INTERPRETATION

Our findings suggest that interorgan communications between the thyroid and liver are disorganized in the early stage of PD, which would be a sensitive diagnostic biomarker for PD. ANN NEUROL 2023;93:303-316.

Thyroid function after diagnostic 123I-metaiodobenzylguanidine in children with neuroblastic tumors

BACKGROUND

Metaiodobenzylguanidine (MIBG) labeled with radioisotopes can be used for diagnostics ¹²³I^-) and treatment (¹³¹I^-) in patients with neuroblastic tumors. Thyroid dysfunction has been reported in 52% of neuroblastoma (NBL) survivors after ¹³¹I-MIBG, despite thyroid protection. Diagnostic ¹²³I-MIBG is not considered to be hazardous for thyroid function; however, this has never been investigated. Therefore, the aim of this study was to evaluate the prevalence of thyroid dysfunction in survivors of a neuroblastic tumor who received diagnostic ¹²³I-MIBG only.

METHODS

Thyroid function and uptake of ¹²³I^- in the thyroid gland after ¹²³I-MIBG administrations were evaluated in 48 neuroblastic tumor survivors who had not been treated with ¹³¹I-MIBG. All patients had received thyroid prophylaxis consisting of potassium iodide or a combination of potassium iodide, thiamazole and thyroxine during exposure to ¹²³I-MIBG.

RESULTS

After a median follow-up of 6.6 years, thyroid function was normal in 46 of 48 survivors (95.8%). Two survivors [prevalence 4.2% (95% CI 1.2-14.0)] had mild thyroid dysfunction. In 29.2% of the patients and 11.1% of images ¹²³I^- uptake was visible in the thyroid. In 1 patient with thyroid dysfunction, weak uptake of ¹²³I^- was seen on 1 of 10 images.

CONCLUSIONS

The prevalence of thyroid dysfunction does not seem to be increased in patients with neuroblastic tumors who received ¹²³I-MIBG combined with thyroid protection. Randomized controlled trials are required to investigate whether administration of ¹²³I-MIBG without thyroid protection is harmful to the thyroid gland.

Durchführung und Befundung der 123I-mIBG-Szintigraphie bei Kindern und Jugendlichen mit Neuroblastom (Version 3) – DGN-Handlungsempfehlung (S1-Leitlinie), Stand: 2/2020 – AWMF-Registernummer: 031-040

Die aktualisierte 3. Fassung der 123I-mIBG-Szintigrafie bei Kindern und Jugendlichen berücksichtigt folgende aktuelle Entwicklungen: Die Leitlinie fokussiert auf die diagnostische Anwendung von 123I-mIBG beim Neuroblastom. 131I-mIBG kommt bei der Radionuklidtherapie zum Einsatz. An wenigen Stellen wird auf Besonderheiten des 131I-mIBG bei der Befundung von Posttherapie-Szintigrammen eingegangen. Es werden aktuelle Entwicklungen in der Patientenvorbereitung bei den Medikamenteninterferenzen und Empfehlungen zur Schilddrüsenblockade berücksichtigt. Neue Empfehlungen der zu applizierenden Aktivität werden genannt und die damit assoziierten Probleme diskutiert. Die Bildakquisition unter Berücksichtigung von SPECT bzw. SPECT/CT des Körperstammes inkl. des Kopfes wird berücksichtigt. Die Befundung unter Verwendung des SIOPEN-Scores wird neu aufgenommen. Auf PET bzw. PET/CT mit 18F-DOPA bzw. 68Ga-DotaTATE wird verwiesen.

Misdiagnosis of Paraganglioma by 123I-mIBG Without Stable Iodine Blockade of Thyroidal Radioiodine Uptake

Iodine-123/iodine-131 (¹²³I/¹³¹I)-metaiodobenzylguanidine (mIBG) scan is an established tool for the localization and treatment of neuroendocrine tumors such as paragangliomas (PGL). To minimize thyroid irradiation by the radioactive iodine in the mIBG preparation, blockade of thyroidal iodine uptake with high doses of stable iodine used to be given routinely as part of all mIBG protocols. As ¹²³I is now more frequently utilized than ¹³¹I, concern about thyroid radiation has lessened and thyroid blockade is often considered unnecessary. However, in certain situations, the lack of thyroid blockade can significantly impact treatment decisions. This report describes 2 patients who had mediastinal masses incidentally discovered on CT scans, and on further evaluation were found to have symptoms suggesting catecholamine excess with mildly elevated plasma normetanephrine levels. ¹²³I-mIBG scans were performed without thyroid blockade, which demonstrated accumulation of tracer in the masses that were therefore deemed positive for PGL. Both patients underwent surgical resection of the masses with their surgical pathology revealing ectopic thyroid tissue (ETT). These cases illustrate that if appropriate thyroid blockade is not performed, ETT concentrating radioiodine from mIBG can lead to falsely positive mIBG scans and unnecessary surgical procedures. We conclude that in the setting of a mass suspicious for PGL in a location potentially representing ETT, such as the mediastinum, thyroid blockade should be employed for mIBG protocols to avoid false positive scans caused by ETT.

Different uptake of 123I-MIBG in the two main liver lobes: A persistant unsolved mistery

PURPOSE

After radiopharmaceutical injection, a heightened ¹²³I-MIBG concentration is frequently observed in the left hepatic lobe compared to the right one, but the reason of this finding remains unknown. Our aim was to retrospectively analyze the different ¹²³I-MIBG uptake pattern between the two hepatic lobes and correlate our results with some epidemiological/clinical features.

MATERIAL AND METHODS

Ninety-four ¹²³I-MIBG scintigraphies from 71 patients were selected. Regions of interest were drawn in the right and left lobes using transverse tomographic sections and left to right activity ratios (L/R ratio) were calculated at 6 and 24h after radiotracer administration.

RESULTS

Twenty-seven examinations were positive for hypermetabolic lesions while the remaining 67 were negative. In all cases mean early and delayed L/R ratios were greater than 1.00; average early L/R ratio was 1.37 and delayed L/R ratio 1.52. The delayed L/R ratio was significantly higher than the early one. There was no difference in the L/R ratios with regard to age, gender, primary disease and result of scintigraphy.

CONCLUSIONS

¹²³I-MIBG uptake was higher in left hepatic lobe compared to right and this ratio did not correlate with any epidemiological or clinical feature. The reason of this metabolic is not yet explained and some biomolecular hypotheses could be tested in 3D dynamic in vitro models.

Imaging Parkinson's disease below the neck

Parkinson's disease is a systemic disorder with widespread and early α-synuclein pathology in the autonomic and enteric nervous systems, which is present throughout the gastrointestinal canal prior to diagnosis. Gastrointestinal and genitourinary autonomic symptoms often predate clinical diagnosis by several years. It has been hypothesized that progressive α-synuclein aggregation is initiated in hyperbranched, non-myelinated neuron terminals, and may subsequently spread via retrograde axonal transport. This would explain why autonomic nerves are so prone to formation of α-synuclein pathology. However, the hypothesis remains unproven and in vivo imaging methods of peripheral organs may be essential to study this important research field. The loss of sympathetic and parasympathetic nerve terminal function in Parkinson's disease has been demonstrated using radiotracers such as 123I-meta-iodobenzylguanidin, 18F-dopamine, and 11C-donepezil. Other radiotracer and radiological imaging methods have shown highly prevalent dysfunction of pharyngeal and esophageal motility, gastric emptying, colonic transit time, and anorectal function. Here, we summarize the methodology and main findings of radio-isotope and radiological modalities for imaging peripheral pathology in Parkinson's disease.