Previous studies have indicated an association between vitamin D and thyroid- and parathyroid-related diseases. However, it remains unclear whether it is a cause of the disease, a side effect of treatment or a consequence of the disease. The Mendelian randomisation (MR) study strengthens the causal inference by controlling for non-heritable environmental confounders and reverse causation. In this study, a two-sample bidirectional MR analysis was conducted to investigate the causal relationship between serum vitamin D levels and thyroid- and parathyroid-related diseases. Inverse variance weighted, weighted median and MR-Egger methods were performed, the Cochran Q test was used to evaluate the heterogeneity and the MR-PRESSO and MR-Egger intercepts were utilised to assess the possibility of pleiotropy. The Bonferroni-corrected significance threshold was 0·0038. At the Bonferroni-corrected significance level, we found that vitamin D levels suggestively decreased the risk of benign parathyroid adenoma (OR = 0·244; 95 % CI 0·074, 0·802; P = 0·0202) in the MR analyses. In the reverse MR study, a genetically predicted risk of thyroid cancer suggestively increased the risk of elevated vitamin D (OR = 1·007; 95 % CI 1·010, 1·013; P = 0·0284), chronic thyroiditis significantly increased the risk of elevated vitamin D (OR = 1·007; 95 % CI 1·002, 1·011; P = 0·0030) and thyroid nodules was significantly decreased the vitamin D levels (OR = 0·991; 95 % CI 0·985, 0·997; P = 0·0034). The findings might be less susceptible to horizontal pleiotropy and heterogeneity (P > 0·05). This study from a gene perspective indicated that chronic thyroiditis and thyroid nodules may impact vitamin D levels, but the underlying mechanisms require further investigation.

The history of the parathyroid glands is a fascinating one full of famous medical names. The discovery of the glands was followed by laborious research into their anatomy, embryology and pathology and into the physiology of calcium metabolism; this led to the manufacture of hormone substitutes and, finally, to the refinement of surgical techniques. The glands were first identified in 1850 by Sir Richard Owen, conservator of the Hunterian Museum, but it was not until 1880 that the term ‘glandulae parathyroideae’ was first used. The physiology of parathyroid hormone and calcium metabolism eluded physicians and the forefathers of thyroid surgery alike for several decades more. Patients were treated as curiosities and were documented as untreatable medical patients or as inexplicable thyroid surgery complications. Halsted noticed the ‘disastrous results from the loss of the glands’ and the resulting tetany, as did Billroth. It is the patients, however, who best illustrate the journey of discovery. In this review, we discuss three cases, highlighting their contributions.

The parathyroid glands are small, inconspicuous, and variable in number, colour and position. Their identification is vital for excision of hyper-functioning glands and for preservation of normally functioning ones in patients undergoing thyroidectomy.

Intravenous infusion of methylene blue at a dose of 7.5 mg/kg is commonly used to aid visualization of the parathyroid glands intra-operatively. Methylene blue is generally considered benign, and there are only two cases published in the literature reporting toxicity following intravenous infusion – such toxicity is a diagnosis of exclusion.

We report a case of methylene blue toxicity resulting in expressive aphasia, confusion and disinhibition following infusion for parathyroid adenoma localization. The patient made a complete recovery over 48 hours. Methaemoglobinaemia was excluded as a cause. We suggest that the mechanism of toxicity was a direct effect of methylene blue, although an adverse interaction with serotonin re-uptake inhibitors could not be excluded.

In keeping with the UK National Poisons Information Service recommendations, we have altered our practice and now use methylene blue at a dose not exceeding 4 mg/kg. This has not affected our success rate for identification of parathyroid glands. We report this case to highlight the rare occurrence of methylene blue toxicity when used at a dose of 7.5 mg/kg.

Primary hyperparathyroidism during pregnancy carries significant risks to both mother and fetus. Parathyroidectomy remains the only definitive treatment for the condition. The timing of surgery remains controversial, with ongoing debate regarding the safety of surgery during the third trimester. A case of symptomatic primary hyperparathyroidism treated by parathyroidectomy in the third trimester is described. The clinical features, investigations and treatment options are discussed.

This paper describes the use of the Neurosign 100 Nerve Monitor and vagus nerve stimulation in the identification and assessment of the integrity of the recurrent laryngeal nerve (RLN) during thyroid and parathyroid surgery.

Vocal fold function was assessed pre- and post-operatively in all patients undergoing thyroid and parathyroid surgery. The nerve monitor, used in association with endotracheal electrodes, was used to confirm correct RLN identification and demonstrate its integrity at the completion of surgery.

There were 21 unilateral and 19 bilateral neck explorations. In these 40 patients, 57 of 59 RLNs were identified. The nerve monitor demonstrated RLN continuity in all but one case (equipment failure: electrode misplacement) after initial identification. Vagus nerve stimulation was performed in 21 patients without adverse sequelae. Damage to the RLN was identified in one of these patients, in whom direct RLN stimulation close to the larynx had failed to indicate discontinuity. Post-operatively this patient had a transient unilateral vocal fold palsy.

The use of the Neurosign 100 Nerve Monitor is no substitute for meticulous surgery. Stimulation of the vagus nerve may be a more sensitive means of assessing RLN integrity during thyroid and parathyroid surgery than stimulation of the RLN itself. Confirmation of RLN integrity allows the surgeon to proceed with confidence to the contralateral side of the neck during hazardous bilateral explorations.

Parathyroid cysts are rare. Most of them present in the anterior neck as cystic neck swellings. A case of cervical parathyroid cyst is presented, along with a brief review of the literature regarding the aetiology, clinical features, diagnosis and management of this condition.

Spontaneous massive haemorrhage form a parathyroid adenoma is rare. It can cause extensive cervical ecchymosis as well as compression of structures within the neck. We present a case, discuss the diagnostic features and review the literature