Hypoparathyroidism is a disease associated with parathyroid hormone deficiency as a result of loss or insufficient function of the parathyroid glands, which is manifested by hypocalcemia syndrome. Hypoparathyroidism of various origins occurs in 0.2–0.3% of the population.
Classification of hypoparathyroidism
There is the following classification.
1. Postoperative hypoparathyroidism.
2. Idiopathic (autoimmune) hypoparathyroidism:
2) in the frame of autoimmune polyglandular syndrome 1 – 10 types.
3. Hypoparathyroidism as a result of parasite damage
visible glands as a result of irradiation, exposure to infectious factors, with amyloidosis, hemorrhages into a hormonally inactive tumor of the gland.
4. Aplasia of the parathyroid glands and thymus.
The most common form is postoperative hypoparathyroidism. At the same time, it develops not so much as a result of complete removal of the glands, but rather due to the disruption of their blood supply due to the appearance of cellulose fibrosis in the surgical area.
In qualified surgeons operating on the thyroid gland, the number of cases of postoperative hypoparathyroidism should not exceed 2%, and during repeated operations – 5-10%.
Sporadic forms of idiopathic hypoparathyroidism occur, as a rule, in young people. A rare disease in which hypoparathyroidism occurs is Di George syndrome (Di George). In this syndrome, the genesis of the parasitic glands is combined with aplasia of the thymus and congenital heart defects. A rare cause of hypoparathyroidism is the destruction of the parathyroid glands by tumor infiltration in the neck region, as well as in hemochromatosis and amyloidosis.
In premature infants, neonatal transient hypoparathyroidism occurs, which is associated with the underdevelopment of the parathyroid glands. Functional forms of hypoparathyroidism occur with long-existing hypomagnesemia. The latter develops with magnesium malabsorption (with malabsorption syndrome, chronic alcoholism), and long-term diuretic therapy.
The lack of parathyroid hormone leads to an increase in the level of phosphorus in the blood due to a decrease in the phosphaturic effect of parathyroid hormone on the kidneys, as well as hypocalcemia due to a decrease in calcium absorption in the intestine, a decrease in its mobilization from the bones and insufficient reabsorption in the renal tubules.
Thus, a distinctive feature of hypocalcemia in hypoparathyroidism is its combination with hyperphosphatemia. In other diseases occurring with hypocalcium (deficiency or resistance to vitamin D), secondary hyperparathyroidism and, thus, hypophosphatemia develops.
Hypocalcemia and hyperphosphatemia lead to a universal impairment of the permeability of cell membranes and thus to an increase in neuromuscular excitability and convulsive readiness, vegetative lability, and the deposition of calcium salts in the internal organs and walls of large vessels.
The main clinical manifestations of hypoparathyroidism are caused by hypocalcemia and hyperphosphatemia, which lead to an increase in neuromuscular excitability and general vegetative reactivity, increased seizure activity.
Distinguish between latent and manifest forms of hypoparathyroidism.
Latent hypoparathyroidism occurs without visible external symptoms and is clinically manifested only by the action of provoking factors or is detected by a special study.
The classic symptoms of hypoparathyroidism are thetacritic convulsions of skeletal muscles in combination with paresthesias and various autonomic disorders, as well as trophic disorders.
Convulsive contractions of skeletal muscles (hypocalcemic tetany) in idiopathic form occur in 75% of cases, and in the postoperative form – in 40% of cases. Paresthesias and fibrillary twitches transform into painful tonic spasms that occur with a preserved consciousness, symmetrically involving the flexors of the extremities, facial muscles (“hand of an obstetrician”, “horse foot”, “fish mouth”), less often – flexors of the back ( opisthotonus).
Tails symptoms (contraction of mimic muscles when tapping at the exit (n. Facialis) and Trusso (appearance of the obstetrician’s hand after 2-3 minutes after shoulder compression with a cuff of the tonometer) are classic and often occurring, but not specific, symptoms of hypoparathyroidism. Smooth muscle spasms they manifest as laryngeal and bronchospasm, dysphagia, vomiting, diarrhea, and constipation. Vegetative manifestations of hypoparathyroidism are characterized by fever, chills, palpitations, and pain in the region of the heart.
The equivalent of tetanic convulsions can be epileptic seizures. In this regard, patients are often mistakenly diagnosed with epilepsy.
There are no specific ECG changes in hypocalcemia; as a rule, the elongation of the Q — T intervals is determined.
In patients with hypoparathyroidism, an ophthalmologic examination can be detected atarakta, and with magnetic resonance tomography of the head – calcification of the basal ganglia. In itself, the calcification of the basal ganglia (Farah’s disease) is an accidental finding in computer and magnetic resonance tomography in elderly patients.
Calcification of the basal ganglia is often clinically manifested by extrapyramidal symptoms with choreoathetosis or parkinsonism.
Other trophic disorders often encountered in hypoparathyroidism include impaired growth of hair and nails, defects in tooth enamel, dry skin, and osteosclerosis.
Laboratory diagnostics is based on the identification of hypocalcemia and hyperphosphatemia, which, at normal levels of creatinine and albumin, make the diagnosis of hypoparathyroidism very likely. In addition, hypoparathyroidism detected hypomagnesemia, hypercalciuria, decreased urinary excretion of phosphorus and cAMP, a decrease in the plasma level of intact parathyroid hormone. In response to the introduction of parathyroid hormone to the patient during hypoparathyroidism, the excretion of phosphate in the urine is increased tenfold (Elsworth-Howard’s test).
Hypoparathyroidism is differentiated with other diseases that occur with convulsive syndrome, as well as with a large group of conditions and diseases accompanied by hypocalcemia.
In all full-term newborns, with the development of hypocalcemia, it is necessary to examine the level of calcium in the blood plasma of the mother in order to exclude her subclinical hyperparathyroidism. In this case, hypercalcemia in the mother can lead to suppression of the function of the parathyroid glands in the fetus.
In patients undergoing surgery on the thyroid gland, it is necessary to differentiate resistant and transient hypoparathyroidism.
The cause of transient hypoparathyroidism, the duration of which, as a rule, does not exceed 4 weeks, is likely to be reversible disturbances in the blood supply to the parathyroid glands, as well as the release of excess calcitonin into the blood.
Both with persistent and transient postoperative hypoparathyroidism, hypocalcemia develops in combination with a shipwreck syndrome already for the first two days after the operation.
If after surgery hypocalcemia combined with the absence of an adequate rise in the level of parathyroid hormone persists for more than 4-12 weeks, we can speak about the development of persistent postoperative hypoparathyroidism.
Until that time, patients are advised to prescribe mono-therapy with calcium preparations and only when confirming persistent hypoparathyroidism to add vitamin D preparations.
Severe hypocalcemia can develop with acute and extensive disintegration of large cell masses. Typical clinical situations in which this is observed are acute pancreatic necrosis, tumor disintegration during successful cytostatic therapy of malignant tumors, severe rhabdomyolysis after injuries, severe convulsive seizures, and intoxication.
In this case, in addition to severe hypocalcemia, hypophosphatemia, a high level of intracellular enzymes (lactate dehydrogenase, creatinine kinase) and uric acid are detected, and pronounced acidosis is noted.
Many of the symptoms of hypoparathyroidism can occur with so-called hyperventilation tetany. In this regard, in the initial diagnosis of idiopathic hypoparathyros, it is advisable to examine the gas composition of the blood.
The treatment of hypoparathyroidism is subdivided into the relief of a therapeutic hypocalcemic crisis and supportive therapy.
To relieve tetanic crisis, intravenous administration of 10–20 ml of 10% calcium gluconate solution, 10 ml of which contains 90 mg of elemental calcium, is used. Calcium gluconate is recommended to be injected slowly, with a speed of no more than 2 ml / min.
With an increase in the level of calcium in the blood plasma to 2 x mmol / l or more, the symptoms are usually stopped. With special care, calcium preparations are administered to patients receiving cardiac glycosides; in this case, intravenous administration is not recommended.
For chronic maintenance therapy of hypoparathyroidism, calcium and vitamin D preparations are used. At first, an attempt should be made to administer calcium monotherapy.
In many patients, it is thus possible to achieve satisfactory compensation of the disease, and there are no problems with possible complications of therapy with Vitamin D.
Among the preparations of calcium salts, gluconate, citrate, lactate, chloride, and carbonate can be prescribed. In determining the dose of the drug is of fundamental importance the content of elemental calcium in a particular salt. Thus, 1 g of elemental calcium is contained in 2.5 g of calcium carbonate, in 5 g of calcium citrate, 4 g of calcium chloride, and 11 g of calcium gluconate.
The usual maintenance dose is 1.0-1.5 g of elemental calcium per day. If it is impossible to compensate for the disease with calcium supplements, supplement vitamin D supplements.
The control parameters in the treatment of hypoparathyroidism are the level of calcium in the plasma blood and its excretion level with urine.