laboratorial correlation of postoperative hypocalcemia after extensive thyroidectomy

The medicai records of 84 patients submitted to extensive thyroidectomy from January 1991 to April1995 were reviewed and the data was analyzed in order to verify a correlation between postoperative laboratories results and physical findings suggestive of hypocalcemia. It was verified that there was hypocalcemia in 51.2 percent of the patients, of which only 18.6 percent presented symptonis. It was concluded that asymptomatic hypocalcemia is frequent in extensive thyroidectomy and a routine screening for serum calcium in the postoperative period following thyroidectomy and calcium reposition must be systematic.


INTROOUCTION
T he thyroid can be affected by many diseases which can be treated by surgery.The extent of surgical resection of the thyroid gland has been dictated by the pathology and the site of the disease.Thyroidectomy lnay cause various complications,I-4 one of which is hypocalcelnia.lt is not unusual for patients undergoing operative procedures on the thyroid gland to experience a transient 01' pernlanent drop in serUln calciuln following operation.
The causal lnechanisln of this hypocalcelnia has still not been cOlnpletely elucidated; however, this lnetabolic disorder is attributed to surgical dalnage inflicted on the parathyroid glands during thyroidectolny; for example, devascu larization, tralllna 01' exeresi s, .01' to local postoperative cOlnplications such as compromise of the blood supply of the parathyroid, I.2,ó-IO edema, hematomas, and infectionY Other causes such as parathyroid suppression due to reabsorption of bone calcium in hypelthyroidism patients, an increase in renal excretion of calciunl due to .postoperative helnodilution, an increase in the reIease of calcitonin resulting from thyroid gland lnanipuIation, the Ioss of bone calcium in thyrotoxic osteodystrophy patients, and autoilnnlune fibrosis of the blood supply of the parathyroid gland are also iInplicated in the etiology of hypocalcemia, but need further confinnation.
Hypocalcelnia is more frequent in extensive thyroidectomy when compared to lninor resections of the thyroid gland, in the ligation ofthe inferior thyroid artery,2 and has been related to the surgeon's experience.Caknlakli et aI., II in a prospective study, reported no difference with and without bilateralligation of the inferior thyroid artery in subtotal thyroidectomy.
The objective of this papel' is to verify if present physical findings are present in postoperative hypocalcelnia and to analyze its incidence.

CASES ANO METHOO
The lnedical records of 84 patients who underwent extensive thyroidectomy between January 1991 and April 1995 were reviewed and statistically analyzed in the Head It included only patients who underwent extensive thyroidectolnies who had postoperative total seruln calciuln Ineasure.Total thyroidectolny and bilateral and unilateral subtotal thyroidectomies associated with contralateral hemithyroidectomy were considered extensive thyroidectomies.
Total serum calciuln was measured in the itnnlediate postoperative period or on the first day.The tneasure of seruln calciuln was made using the ortocresoftalein-complexone Inethod without deproteinzation by espectrophotometer.
Hypocalcetnia was deemed existent when total serum calcium was lower than 8.5 Ing/dI.12  Seventy-nine patients were female (94.1 percent) and just 5 were Inale (5.9 percent), being 15 black, 68 white and 1 Asian.The Inedium age was 44 with a range of ] 5 to 73 years (Graphics 1 and 2).
Fifty-eight (69 percent) patients were submitted to total thyroidectotny, 17 (20.The unilateral subtotal thyroidectomy associated with contralateral hemithyroidectomy was the tnost prevalent surgical resection causing hypocalcetnia.It occllrred in 66.6 percent (6/9) of the cases, followed by total thyroidectolllY in 53.4 percent (31/58) and by bilateral slIbtotal thyroidectomy in 35.3 percent (6/17).The statistical analysis performed showed no significant difference between the occurrence of hypocalcetnia when cOlnpared to different surgical procedures (p>0.05)(Table I).
Histopathologic results were shown in Graphic 4. Statistical analysis was perfonned using the chisquare technique.Both have the same physical findings and the same treatment, the only difference is the time of evolution of more or less than 60 days.In the present paper, hypocalcelnia was not divided into these two groups (pennanent or transitory).We found a higher incidence of hypocalcemia than that described in the literature,2.4.5.7.9.lo,.12-14although the reported frequency varies from 0.2 to 83 percent. 5.ó Hypocalcemia creates a great de aI of apprehension on the part of the physician because of immediate and long-term complications.'5 Chronic complications .areintracranial calcifications, particularly of the basal ganglia, various mental disturbances, such as irritability, depression, and even psychosis.Papilledema and other signs of increased intracranial pressure have been reported.Chronic hypocalcemia may lead to cataract formation, abnormalities of the skin, nails and hair, candida infections and dermatology anomalies.Cardiac effects of hypocalcelnia include prolongation of the QT interval and, rarely, congestive heart failure.Dental anomalies depend on the age at onset; in children hypocalcemia can cause enamel hypoplasia and failure of the adult teeth to erupt.1ó Murakatni 13reported that inorganic urine phosphate is a predictive factor in the diagnosis of immediate or long-term hypocalcemia.
Low leveIs of inorganic urine phosphate are observed in the permanent hypocalcemia of Graves' Disease.
The incidence ofhypocalcemia in total thyroidectolny was not higher than in subtotal thyroidectomy.

DISCUSSION
The incidence of hypocalcemia in patients with malignant disease was higher (60.7 percent) than those with benign disease (46.4 percent).An analysis of hypocalcemia revealed no statistically significant difference between these groups, p>0.05 (Table 2).Hypocalcemia was treated in 14 patients (32.5 percent) with intravenous infusion of 10 percent calcium gluconate solution, oral calcium chloride, or both.In some patients, the laboratory results were obtained in the first ambulatory return wherein hypocalcemia was treated.

N°%
As the extent of the resection of the thyroid increases, the risk of complications such as hypocalcemia and vocal cord paralysis also increase.This is due to bruising, exeresis, and compromise of the blood supply of the .parathyroid gland . 1  Postoperative hypocalcemia can be classified as transient or permanent, the latter lasting more than 60 days5 not agree with the literature.1.7Hemithyroidectolny plus subtotal contralateral thyroidectomy was the most frequent procedure associated with hypocalcemia in the present series.The occurrence ofhypocalcemia was not influenced by the malignant potential of the disease.
La Gamma found 49 percent of asymptomatic hypocalcemia in his study, while McHenry found 67.9 percent.In this study, asymptomatic hypocalcemia was found in 81.4 percent.When the balance between ionized and protein-bound calcium is acutely altered, the symptoll1s may be precipitated. 13ypocalcemia folIowing extensi ve thyroidectoll1Y must always be investigated because of the infrequent symptoms and grave complications if there is not adequate repositioning.

4 -
TT = total thyroidectomy; SBT= subtotal bilateral thyroidectomy; USCHT = unilateral subtotal + contralateral hemithyroidectomy Graphic 3-Clinicai and laboratorial correlation of postoperative hypocalcemia after extensive thyroidectomyWe concluded that hypocalcemia is frequent in the postoperative of extensive thyroidectoll1Y but physical findings are uncommon, and thus foIlowing extensive thyroidectomy, serum calcium investigation is mandatory.Clinicai and laboratorial correlation of postoperative hypocalcemia after extensive thyroidectomy

Table 2
Postoperatory hypocalcemia and histopathologic results in 84 patients submitted to extensive thyroidectomy.

Table 1
Surgery resection and hypocalcemia correlation in 84 patients submitted to extensive thyroidectomy.