SAT-390 - Coexistence of Latent Autoimmune Diabetes in Adults and Thyroid Hormone Resistance Syndrome: A Case Report

LADA (Latent Autoimmune Diabetes in Adults) is associated with other autoimmune disorders. Thyroid autoimmunity (TA) is the most common in LADA patients with the reported co-association 22.1% to 33.3%. LADA accounts for 8-10% of adult-onset diabetes cases globally.
Thyroid Hormone Resistance (RTH) is a rare genetic syndrome, mostly due to mutations in the thyroid hormone receptor β (THRB) gene with an estimated prevalence of 1 in 50,000 live births.
While RTH can co-exist with TA more frequently, we have found no published clinical cases of RTH coexisting specifically with LADA.
This is a clinical case of 37-years old male patient.
In December 2024 routine check-up identified blood glucose levels 16 mmol/L, HbA1c 9.40% and C-peptide 0.5 ng/ml. Given LADA in patient’s mother, he was diagnosed with LADA and put on basal-bolus insulin therapy. Screening for TA revealed elevated TSH, free T4 and free T3 levels, normal TSH receptor antibodies (TRAb) and no clinical signs of thyrotoxicosis. No structural abnormalities were found on thyroid ultrasound (TU). Head MRI showed 4 х 4 х 3 mm pituitary microadenoma.
In May 2025 the patient was admitted to the Endocrinology Research Center, Moscow, Russia for preoperative preparation with TSH-secreting microadenoma preliminary diagnosis. He presented with slight weight loss (3-4 kg) over the past few months, sweating and hands tremor.
Lab evaluation confirmed central thyrotoxicosis - elevated free T4 29.5 pmol/L and free T3 10.3 pmol/L, normal TSH 2.2 mU/L and TRAb 0.84 U/L. Tissue thyrotoxicosis markers were in reference range SHBG 29.0 nmol/L, Osteocalcin 14.7 ng/mL. Additional lab work-up - elevated GADA 377.65 U/mL and IA-2 104.47 U/mL, normal ICA 0.24 U/mL and IAA 3.55 U/mL, total cholesterol 5.3 mmol/L and LDL 3.1 mmol/L.
The patient was clinically euthyroid. Sinus bradycardia was on EKG, heart rate 58 bpm. Lumbar spine and proximal femur BMD was age-appropriate on DXA scan. TU revealed neither thyroid nodules nor thyroid goiter. Pituitary microadenoma 3,5 mm maximum in size was verified on contrast-enhanced MRI and confirmed hormonally silent.
Considering clinical course and lab findings discrepancies, RTH was suggested. Firstly, patients’s mother aged 57 for the first time was screened for TA and turned out to have elevated free T4 26.2 pmol/L, free T3 9.74 pmol/L, normal TSH level 3.45 mU/L and no clinical evidence of thyrotoxicosis. Secondly, THRb gene Sanger sequencing identified heterozygous variant in the THRb gene (NM 001354712.2) in exon 10 (HG38, chr3-24127631 G>A, c.1012C>T), p.Arg338Trp (rs121918697; HGMD:CM930706; pathogenic; PMID:21871106, 23926384).
To our knowledge, this is the first published case of RTH and LADA co-existance. Pituitary adenomas with central thyrotoxicosis should be scrutinized for differential diagnosis of TSH-secreting adenoma vs RTH with drastically different therapeutic options to be made.

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