Parathyroid

1- PTH:

* The effect on bone: PTH increases bone resorption (increased hydroxyproline); the bone response to PTH is biphasic. In the second stage, the bone resorption and formation are both increased. resorption winning in general on training

* On bone cell, PTH stimulates adenylate cyclase and increase the Ca ++ influx into the cell.

* PTH increases production of lactate and especially citrate (which is a good sign of bone resorption).

* The PTH stimulates the 1-α-hydroxylation of the 25-OH-vitamin D3 in the kidney

* The PTH increases the intestinal absorption of Ca ++ indirect way (-> vitamin D3)

* The PTH increases the intestinal absorption of phosphorus; it increases phosphaturia by declining phosphorus reabsorption => hypophosphatemia.

* Other action on the kidney: increased reabsorption of magnesium and excretion of K +, Na +, bicarbonates and urinary pH elevation.

* On the lens: reduces PTH => glycolysis = the disorder> cataract

* On the pancreas: high PTH secretion of gastrin by cells D => recurrent ulcer in some hyperparathyroidism

A- Calcitonin:

* The main stimulus of CT secretion is hypercalcemia; others: penta-gastrin (and CCK)

* The pentagastrin test is used in the diagnosis of medullary thyroid cancer secreting calcitonin.

B- Vitamin D:

* In the bone, the calcitriol (1,25-dihydrocolécalciférol) acts primarily on bone-téoclastes. Antirachitic The effect of vitamin D is made by making available a large amount of calcium for mineralizing reactions. PTH is synergistic vitamin D.

2- Hyperparathyroidism:

A- Primary hyperparathyroidism:

* The single adenoma is the most common cause (80%); in 10% of adenomas are located in ectopic parathyroid (mediastinum, neck, retro-oesophageal space).

* Hyperplasia of the parathyroid glands (15-20%) covers all four parathyroid glands. Type 2a NEM (syndrome Sipple: + medullary thyroid cancer + pheochromocytoma). NEM type I (Wermer syndrome)

Disorders related to movement of calcium:

* In the bone level: geodes; bone pain, swelling and pathological fracture.

* In the kidney; nephrolithiasis, nephrocalcinosis

Disorders related to the action of calcium in the tissues:

* Increase of the action potential threshold (cell hypoexcitailité): muscle weakness, fatigue, shortening of QT;

* Digestive tract: dysphagia, nausea, vomiting, constipation, abdominal pain and cramping-minales

* At nervous level: psychasthenia, confusional disorders, depression, headache

* The polyuropolydipsic syndrome is very common and early (moderate 2 to 3 L / d); urine are hypodense (poor concentration of urine). This polyuria is insensitive to ADH.

* Renal failure is the major risk of progression

* The swellings are exceptional; They often sit on the jaw

* The bone lucency is diffuse, more marked at the cortical level (blur edge and enlargement of the spinal canal); tuft appearance before the ends of phalanges. Bleached skull of internal and external tables with “hairy appearance” (microgeodes).

* The geodes association (with a punch without condensation around) and de-mineralization is the fibrocystic osteitis Recklinghausen

* Neuropsychological Event: apathy, asthenia

Events * Digestive: anorexia, nausea, constipation are common. Recurrent ulcer of the stomach; calcific pancreatitis.

* Other: HTA;

B- biological signs:

* Hypercalcemia (between 2.57 to 2.75 mmol / L)

* The absence of hypercalciuria is possible and does not reject the diagnosis

* The hypophosphatemia is a sign of major importance

* Phosphorus reabsorption is always <80%

* Elevation of cAMP nephrogenic

* Elevated blood citrate; increased alkaline phosphatase: increased hydrocyprolinurie

* Dynamic test: calcium infusion test (calcium deprivation is abandoned).

C- The bone biopsy:

Two fundamental lesions bone resorption process and increase osteo blast activity with emphasis fibrous tissue

Location of the tumor:

* Cervical ultrasonography has value only if positive

* Cervical CT has no interest; this examination seems useful here to locate mediastinal adenomas.

* The most powerful examination is sestamibi scintigraphy

D- Clinical forms:

* Asymptomatic hyperparathyroidism

* Hyperparathyroidism with renal impairment urinary calcium and calcium levels are normal (in renal failure serum calcium is low)

* Tertiary Hyperparathyroidism: thyroid hyperplasia which follow the secondary hy-perparathyroïdies and become autonomous.

* Acute hypercalcemic crisis: significant confusion,

E- Causes of hypercalcemia:

1- malignant hypercalcemia:

* Bone Metastases

* Myeloma

* Paraneoplastic hypercalcemia

* Hematologic malignancies

2- exogenous hypercalcemia:

* Overdose of vitamin D, calcium

* Thiazide diuretics

* Vitamin A

* Burnett Syndrome (abuse of milk and alkaline)

3- Other causes:

Sarcoidosis *

* Addison’s Disease

* Hypothyroidism; hyperthyroidism

* Prolonged immobilization

Treatment:

Formal indication for surgery in case of adenoma; hyperplasia and in case of tertiary hyperparathyroidism.

3- hypoparathyroidism:

A- true Hypoparathyroidism:

* Traumatic: surgery

* Congenital: Di George syndrome

* Autoimmune: Whitaker syndrome (adrenal insufficiency + + moniliasis)

* Transient: newborn to a mother hypercalcémique-

B- Pseudohypoparathyroidism:

* This device is a non-responsiveness to PTH

* Organic Table of hypoparathyroidism

* Deformities: small, rounded facies brachymétacar-pie, debility, subcutaneous calcification

* PTH is high

– Psuedo-pseudohypoparathyroidism: the dysmorphic syndrome without biological picture of the pseudo-hypoparathyroidism

C- Clinic:

* Paroxysmal manifestations of hypocalcemia: tetany

* Chronic Events:

– Neuromuscular hyperexcitability: Chvostek sign, Trousseau sign,

– Neurological disorders: Parkinson’s disease; choreiform or athetoid movement disorder

– Trophic disorders: desquamation, alopecia, leukonychia streaked teeth caries repeatedly,

– Posterior capsular Cataract

– ECG: increase the QT interval (by increasing ST)

– Heart failure if major hypocalcemia.

D- Causes of hypocalcemia:

– Chronic renal failure

– Malabsorption syndrome, cirrhosis, malnutrition

– Anticonvulsant drugs (barbiturates, phenytoin); rifampicin

– Severe acute pancreatitis;

– Blood Perfusion citrate

– Bone metastases sclerotic

– Medullary thyroid carcinoma (-> calcitonin)