Parathyromatosis (plural: parathyromatoses) is the very rare phenomenon in which there is hyperplasia of residual foci of parathyroidal soft tissue after surgical parathyroidectomy resulting in recurrent hyperparathyroidism.

Epidemiology

Parathyromatosis is very rare, a study from 2012 stated that there were only 35 reported cases in the global English medical literature ². Most reported cases have been in female patients in their 6^th and 7^th decades ³. It is more common in those with chronic renal disease probably as part of long term hyperstimulation of the parathyroid hormone axis ⁴.

Clinical presentation

Parathyromatosis presents as primary hyperparathyroidism with classic manifestations, many related to hypercalcaemia.

• lethargy
• loss of concentration, intellectual impairment
• depression
• nephrolithiasis
• osteoporosis
• constipation
• peptic ulcer disease

Pathology

In very rare cases following the surgical removal of the parathyroid glands, patients relapse with hyperparathyroidism a phenomenon known as parathyromatosis. This is thought to be due to hyperplasia of ectopic parathyroid tissue. There are several ways in which this may occur:

• developmental rests of parathyroid tissue are relatively common in the soft tissues of the mediastinum and neck, often in proximity to normal parathyroid glands
• as a complication of parathyroidectomy
  • surgical spillage of parathyroid tissue during procedure
  • incomplete resection of an abnormal parathyroid gland

It is important to appreciate that in some cases the cause of the recurrent hyperparathyroidism is not parathyromatosis but the presence of supernumerary parathyroid glands which were missed in the original investigation and treatment of the preoperative patient. 

Location

Locations tend to be in and around the neck and chest as per the normal developmental site(s) of the parathyroid glands ⁴.

Common

• thyroid compartment
• sternocleidomastoid muscles

Uncommon

• subcutaneous fat
• next to recurrent laryngeal nerve
• poststernal space
• carotid sheath
• thymus
• superior mediastinum
• tracheoesophageal groove

Microscopic appearance

Histopathological differentiation of parathyromatosis from parathyroid carcinoma may be a challenge for the pathologist ¹. Sometimes, the hyperplastic rests of parathyroid tissue may demonstrate marked fibrotic change with invasion of the adjacent soft tissues and muscle. Cellular mitoses may be a prominent feature. Notably, in contradistinction to malignancy, extension into the vasculature is lacking.

Markers

It is also clear now that the molecular signature of parathyromatosis is akin to benign parathyroid diseases, at least with regards to the synthesis of the proteins parafibromin, Ki-67, RB and galectin-3.

Radiographic features

In parathyromatosis, the ectopic foci of parathyroid tissue are often identified on structural imaging as nodules superficial to the strap muscles in the neck that have been assumed to have been seeded there postoperatively. Occasionally they are found more deeply or remotely as they represent embryological rests rather than a postsurgical sequela. Although sometimes it is extremely difficult to localise the foci, cf. localising parathyroid adenomas.

Ultrasound/CT/MRI

Small hypoechoic hypervascular nodules in a superficial location is the commonest appearance ^3-5. They may have a similar appearance to cervical nodes or even normal parathyroid glands however in the typical clinical context differentiation is usually not difficult ³.

Nuclear medicine

Tc-99m-MIBI scintigraphy/SPECT-CT

Small foci may be overlooked by technetium-99m-sestamibi functional studies. However when seen there is the characteristic delayed tracer uptake ^3,5.

Differential diagnosis

• supernumerary parathyroid glands ¹