Endocrine Abstracts

Background: Primary hypothyroidism diagnosis is mainly based on the TSH (thyroid-stimulating hormone) and free thyroxine (T4) levels. Following treatment initiation, the main lab test used for dose adjustment is TSH. However, there could be potential issues with TSH measurement.

Case report: A young lady, 36, presented to our clinic in January 2019, being treated with Levothyroxine 175 mg daily, and having clinical signs and symptoms of thyrotoxicosis: tachycardia, palpitations, excessive sweating, tremor, increased gut motility, hair thinning and nail softening, menstrual irregularities, insomnia. She was also taking Propranolol PRN to reduce the heart rate.

Her personal history was unremarkable until Feb 2009, when she was diagnosed with primary hypothyroidism at age 26, based on high TSH, 16.8 mU/l, and T4 not sampled at the time of diagnosis. She started Levothyroxine therapy, 100 mg daily, her TSH was followed up periodically and was high (> 10 mU/l) on multiple occasions, apparently not responding to treatment, leading to Levothyroxine dose escalations.

At the time of presentation to our clinic, she got her thyroid function tests sampled and, despite the abnormal TSH value (5.79 mU/l), the Levothyroxine dose was reduced to 125 mg daily, which led to significant improvement in her symptoms, and she stopped Propranolol completely.

Two months later, her TSH was 4.3 mU/l, we then performed a PEG (polyethylene glycol) precipitation of the sample, and the monomeric TSH was obtained at the level of 0.58 mU/l. Since then, we further reduced the dose of Levothyroxine to 100 mg daily, her last TSH was 3.34 mU/l (normal), and she feels well.

Discussion: Our case reminds of the fundamental principle ‘Primum non nocere’.

Treating the blood test result and continuing to increase the dose aiming to normalise the TSH value, without taking into account the clinical presentation, can lead to overtreatment and cause iatrogenic thyrotoxicosis.

We could only hypothesise that the laboratory testing could mislead due to the presence of interfering macromolecules, taking into account that we did not have possibility to perform a gel filtration chromatography, which is considered a gold standard to identify the monomeric TSH. We could speculate that, in some cases, PEG precipitation is a useful tool to identify patients with falsely elevated TSH levels.