Secondary and Tertiary Hyperparathyroidism

DEFINITION

Secondary:
- increased PTH due to external factors that stimulate the glands
Tertiary:
- autonomous hyper-secretion once secondary corrected or when refractory
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EPIDEMIOLOGY

As per cause

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AETIOLOGY

Secondary
- most commonly CRF
- less commonly GI malabsorption, vit D deficiency, osteomalacia, rickets, malnutrition, osteoporosis, hypermagnesuria, idiopathic hypercalciuria

Tertiary
- autonomous hypersecretion

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BIOLOGICAL BEHAVIOUR

Secondary
Gland physiologically responding to hypocalcemia, Vit D deficit, or hyperphosphataemia.
- vit D deficit and hyperphosphatemia in renal failure can contribute to low serum calcium.
- vit D deficit can result from inadequate intake, insufficient sunlight or more commonly CRF (kidneys can't hydroxylate 25-hydroxycholecalciferol to 1,25(OH)2D3)
- hyperphosphatemia is from kidney's inability to excrete phosphorus, retention lowers ionized Ca++ in blood and interferes with 1,25(OH)2D3 production.
--> hyperplasia of all glands
--> reversed with renal transplantation.

Tertiary
After renal transplant, SHPT improves in 95%;
But may persist for 2y or more because of autonomous THPT

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MANIFESTATIONS

As for hyperparathyroidism
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INVESTIGATIONS

Blood tests as per above/below
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MANAGEMENT

Medical
Almost all patients with CRF have secondary HPT, but most can be managed successfully.
- dietary; phosphate restriction if elevated, or wif PTH high range;
- supplementation of Calcium.
- when worse, phosphate binder (e.g. Calcium based), but not so good on dialysis; soft tissue calcification.
--> hemodialysis usually effective and decreasing blood phosphate concs.
Despite good care, some develop worsening bone disease.
- Vit D analogs at this stage can help prevent bone turnover.
Calcimimetics are new drugs that target teh calcium-sensing receptor on the parathyroids.
- v. effective but side effects include severe nausea and vomiting.

Indications for parathyroidectomy
1. Calciphylaxis
- i.e. persistent, refractory hyperclalcaemia
--> soft tissue calcification with ischemia and necrosis
--> painful erythematous skin lesions that can lead to ulcers ; gangrene
- an absolute and emergent indication for surgery
2. SHPT refractory and with:
- PTH > 600 pg/ml
- Ca++ x PO4- > 55
- high-turnover bone disease
3. SHPT consistent with above and associated with:
- subperiosteal absorption
- bone pain
- pathologic fractures
- severe pruritis
- persistent anaemia
- renal osteodystrophy (bone disease in renal failure; fibrosis, cysts, weakness)
- hypercalcaemia
- hyperphosphataemia
- extraskeletal non-vascular calcification (often in vessels, with hypertension, end organ effects)

Indications in THPT
Consider surgery early if renal graft compromised
or bone loss and steroids
or acute pancreatitis
or progressive bone disease

Surgical Management

1. Complete careful preop workup
- coordinated with renal physicians
- dialysis no later than 1d before.

2. Usual approach is bilateral neck exploration
- localizing studies still useful to detemin ectopic or supernumerary glands.
--> if large glands not seen on USS, suspect ectopic glands and do a sestamibi and CT or MRI.

3. Subtotal or Total?
- primarily surgeon dependent decision; both acceptable.
- lower risks of permanant hypoparathyroidism from subtotal
- but total removes risk of persistent or recurrent disease
--> if doing total, should do reimplantation; else risk of adynamic bone disease

4. Post-operative management
Beware hungry bone disease
- increased skeletal calcium deposition and causes severe hypocalcemia.
Transient hypo in ~10% people
- therefore patients all placed on 4-6g/day calcium
- calcitriol 0.5-4ug/day often needed to prevent hypocalcemia.
--> some still may need clacium gluconate for severe deficiency... beware risk of skin necrosis if extravasates.
Correct Mg as well as can aggravate hypocalcemia.

5. Outcomes
Dramatic and immediate
Pruritis improves early; 1/3 report decreased muscle weakness.
Improvement in anaemia in >50%
Overall improves many symptoms and metabolic sequelae, including hypertension, reduces cardiovascular events and results in reduced mortality.

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REFERENCES

Cameron 10th