Simplified minimally invasive invasive parathyroidectomy

We agree with Wong et al that minimally invasive parathyroidectomy (MIP) is a safe and effective option in selected patients (approximately 50% of those with primary hyperparathyroidism) but would like to comment on some aspects of methodology and conclusions as reported in their case series.

The authors quote a reference from 2003¹ to support their assertion that only a small minority of consultant members of the British Association of Endocrine and Thyroid Surgeons (BAETS) were using the lateral incision approach. The third national audit of the BAETS database in 2009 showed that a targeted approach was used in 35% of patients who underwent first time surgery for primary hyperparathyroidism.²

The series by Wong et al reports only on patients in whom MIP was attempted. We assume that there would be other patients with primary hyperparathyroidism who underwent planned bilateral exploration. From an epidemiological perspective (and for readers to obtain a greater insight and perspective into the authors’ practice), it is important that the article includes details of all patients who underwent surgery and the results of imaging in those patients who underwent bilateral exploration. In addition, restricting reporting of accuracy of technetium sestamibi (MIBI) scans and ultrasonography to only those who underwent MIP would grossly exaggerate the tests’ reported success.

In the Methods section, Wong et al state that ultrasonography and/or MIBI scans were used for localisation. A systematic literature review and evidence-based guideline³ confirms our view that unilateral/targeted parathyroidectomy should be used only if MIBI and ultrasonography results are concordant. If parathyroid localisation studies are non-concordant, or only a single scan is positive, the appropriate approach should be bilateral neck exploration or targeted parathyroidectomy with intraoperative parathyroid hormone (IOPTH) assay.

The use of 7.5mg/kg of body weight of intravenous methylene blue is an unnecessarily high dose that has the potential to cause serious neurotoxicity.⁴ The most appropriate ‘maximum permitted dose’ for intravenous methylene blue has been debated in the literature before.⁵ The general consensus and recommendation by the UK National Poisons Information Service is that the dose of methylene blue should not exceed 4mg/kg of body weight.^6,7

The algorithm presented by Wong et al needs further clarification. It seems to suggest that a decision to use IOPTH is made during surgery when a ‘suspicious lesion’ has been found. To use IOPTH in an appropriate and effective manner, a basal sample for PTH should be drawn before incision. Use of this modality during the operation (without a basal sample) may give erroneous and misleading results. Perhaps the authors can further explain their technique and whether this has been validated?

Finally, Wong et al’s argument that ‘MIP has been shown to be the superior approach’ is based on differences in outcomes shown in an observational study where MIP has only been used in ‘selected’ cases.⁸