Statistical analysis was performed using SPSS version 10.0.1 (SPSS Inc, Chicago, IL, USA). Results are shown as mean ± standard deviation (SD). Significant differences between the two groups were determined using either unpaired Student's t test or the Mann-Whitney U test for interval variables when appropriate. Probabilities equal to or smaller than 0.05 were considered to be significant.

The two groups were comparable in terms of age, sex ratio, clinical signs and symptoms, type of pathology and extent of thyroidectomy. Most of the patients were in the age group of 20-60 years. All the patients were females except one male in group A. Indications for surgery included colloid goiter (50%), multinodular goiter (37.5%) and hyperplastic goiter (12.5%). Pre-operative biochemical parameters (T3, T4, TSH, serum calcium, albumin corrected serum calcium, ionic calcium and serum phosphorus) were comparable between the two groups. One patient in group A and 3 patients in group B were hyperthyroid and were rendered euthyroid with anti-thyroid drugs before surgery. All the patients underwent subtotal thyroidectomy leaving about 3-4 grams of residual thyroid parenchyma. In group B, imprint cytology smears revealed parathyroid tissue in 19 (95%) cases while 1 (5%) smear had shown cells of thyroid origin. In this case another parathyroid was dissected out, confirmed with imprint cytology and then autotransplanted. Table-1 shows the number of parathyroid glands identified, cytologically verified and autotransplanted during thyroid resection.

Figure 1

Table 1: Number of parathyroids autotransplanted after cytological verification

Time taken for surgery was 60-140 minutes (90.5 ± 21.97) in group A and 70-120 minutes (91 ± 14.38) in group B and the difference was statistically insignificant (p>0.05). The weight of the resected thyroid gland ranged from 20-300 grams (66.5 ± 66.21) in group A and 20-280 grams (71.85 ± 61.51) in group B and was comparable. No case in either group had postoperative hoarseness of voice suggestive of recurrent laryngeal nerve damage. Clinical hypocalcemia was observed in the post-operative period in almost half the cases of both groups but the difference was not statistically significant (p>0.05). The signs and symptoms of hypocalcemia were more on day 1 and decreased on day 2 and day 3 in cases of both the groups (Table-2).

Figure 2

Table 2: Clinical signs and symptoms of PoH

Biochemical hypocalcemia was observed in 3 cases of group A on post-operative day 1 only and in none of the cases of group B and the difference was not statistically significant (p>0.05). One patient each from group A and group B required parenteral calcium supplementation up to day 5 for management of hypocalcemia. Ten patients (50%) of group A and 14 patients (70%) of group B were discharged on the third post-operative day. Those patients with persistent severe symptoms with or without biochemical hypocalcemia were kept under observation. In group A, prolonged hospitalization was required in 4 patients (20%) up to day 4 and in 3 patients (15%) up to day 5. In group B, two patients (10%) each required prolonged hospitalization up to day 4 and day 5 due to PoH. One patient (5%) each from group A and B required hospitalization up to the seventh post-operative day due to clinical hypocalcemia. None of the patients from either group required prolonged hospitalization due to wound complications.

At 15 days follow-up, 3 cases (15%) of group A and 2 cases (10%) of group B had clinical hypocalcemia although the difference was not statistically significant (p>0.05). At 3 months and 1 year follow-up no case from group B and only one case (5%) of group A had clinical hypocalcemia suggesting permanent PoH. On biochemical analysis, only the patient of group A with permanent PoH had decreased levels of albumin corrected serum calcium on day 15, 3 months as well as 1 year follow up. This 40-year-old female patient had undergone subtotal thyroidectomy for multinodular goiter. Only 2 parathyroids were identified during surgery and the weight of the resected specimen was 50 grams. The patient required parenteral calcium supplementation in the post-operative period for clinical hypocalcemia and was discharged on the 6^th post-operative day with normal biochemical parameters.

Autopsy findings of three patients with PTHAT, who died 2-15 months after surgery, identified PTHAT tissue of the same size on gross examination and confirmed the presence of regenerated parathyroid cells on microscopic examination.₄ The physiological tests have also suggested that the regeneration of glands was complete in 4-5 weeks.₄ It has been proven by selective venous sampling from the forearm after PTHAT that the autotransplanted parathyroids synthesize and secrete parathyroid hormone.₃₃,₃₄

Although experienced surgeons are often able to identify the parathyroid glands, sometimes it is difficult to differentiate them from other contiguous tissues. Intra-venous administration of methylene blue,₃₅ contact endoscopy,₃₆ frozen section₂₉ and intra-operative cytology₃₇ are various methods described for identifying parathyroids. Out of these, intra-operative frozen section and cytology appear to be more practical in approach. Intra-operative frozen section, apart from prolonging the operative time, leads to loss of parathyroid tissue in section preparation. In the present study loss of tissue was avoided by mincing the parathyroid gland over a glass slide and the same slide was used for preparing imprint cytology smear. It did not prolong the surgery since operating time was comparable between the cases of both groups. Moreover, parathyroid tissue was identified in 95% of cases. One case (5%) showing thyroid tissue on imprint smear underwent PTHAT from another parathyroid gland after cytological confirmation during the same procedure. Thus imprint cytology was able to identify parathyroids in 100% cases.

During thyroidectomy all the four parathyroid glands were identified in most of the cases (60% in group A and 55% in group B) on gross examination. In the remaining cases, 1-3 parathyroids were identified. Studies conducted in the past have shown that unnecessary dissection to identify all the parathyroids should be avoided to reduce the incidence of ischemic injury.₁,₃,₄ The same principle has been followed in the present study.

Most of the authors have shown their preference for autotransplanting parathyroid glands in the exposed sternocleidomastoid muscle.₁₂,₁₄,₃₀,₃₈The same principle has been followed in the present study because of the convenience of the procedure. However, other sites used for PTHAT are pectoralis major muscle, cephalad portion of strap muscles and non-dominant forearm. These sites are used especially when staged bilateral modified neck dissection is anticipated and in case of malignancies.₂₉,₃₀

In the literature, there is controversy in the number of parathyroid glands to be autotransplanted to prevent permanent hypoparathyroidism. The frequency of hypocalcemia was found to increase when the number of autotransplanted parathyroids increased.₂₈,₃₈However, Funahashi et al. transplanted 2.94 glands on an average in each case and concluded that transplantation of only one gland leads to permanent hypoparathyroidism and suggested that the higher the number of glands autotransplanted the better would be the outcome.₃₂In the present study, the majority of the patients (85%) had autotransplantation of only one gland and in the remaining cases (15%), two glands were autotransplanted. Most of the workers in the past have also autotransplanted one or two parathyroids.₁₃,₁₄,₁₅,₃₀,₃₈

Lo and Lam (1998) did selective parathyroid autotransplantation only in cases with damaged parathyroid glands with doubtful viability in 36% of the patients of their study. Transient hypocalcemia occurred more often in patients with PTHAT (21%) than without PTHAT (8%), while permanent hypocalcemia occurred only in patients who did not undergo PTHAT (2.6%).₁₂After routine parathyroid autotransplantation, Skinner₃₉ found that only one patient had permanent hypoparathyroidism, while Zedenius₁₄ reported an incidence of 0% for permanent hypoparathyroidism. Results of other workers are shown in Table-3. In the present study, routine PTHAT was done in 20 cases and the incidence of transient and permanent PoH was 10% and 0%, respectively.

Figure 3

Table 3: Incidence of PoH after PTHAT and in situ preservation of parathyroids

In the literature, time duration for deciding onset of permanent PoH ranges from three months to one year.₁₄,₁₅,₂₄,₃₈In the present study, postoperative hypocalcemia was defined as patients requiring medications to maintain normocalcemia when they were discharged from the hospital. Patients were regarded as having transient PoH if they became clinically as well as biochemically normal up to 2 weeks after stopping all medications during follow-up. Postoperatively, hypocalcemia requiring treatment to maintain normocalcemia and to control signs and symptoms at one year follow-up was regarded as permanent PoH.

In the present study, the difference in the incidence of symptoms and signs of PoH between the patients of the two groups was found to be statistically insignificant (p>0.05). However, signs and symptoms of PoH were more frequent on day 1 and day 2 and became less frequent on day 3 in patients of both the groups (Table-2). This is probably because of trauma to the parathyroid glands during operation causing venous congestion severe enough to produce temporary embarrassment of arterial supply and a reversible injury.

All the biochemical parameters were measured preoperatively. Although PTH level is the most sensitive indicator of parathyroid function, it could not be done because of lack of availability of this investigation in our set-up. However, albumin corrected calcium and ionic levels are equally sensitive indicators of parathyroid function and were measured in the present study. The levels were normal in most of the cases and there was no statistically significant difference between the two groups (p>0.05). In our control group cases, albumin corrected calcium levels were low only in 3 patients (15%) on day 1 and in none of the patients (0%) on day 2 and day 3. In the study group, decreased levels of albumin corrected calcium were observed in none of the patients (0%) from day 1 to day 3. This is probably due to the fact that early calcium supplementation was started on clinical findings of PoH leading to normal serum calcium levels in all cases of PoH in both groups.

The incidence of transient PoH was 15% in the control group and 10% in the study group while the incidence of permanent PoH was 5% in the control group and 0% in the study group. The incidence of transient and permanent PoH as reported by other authors is shown in Table 3. In previous studies, the incidence of transient as well as permanent PoH is much higher probably because a large number of cases in them had thyroid malignancies which required near total/total thyroidectomy while the present study dealt only with benign thyroid lesions requiring subtotal thyroidectomy. These observations prove that PoH can occur following surgery for malignant as well as benign thyroid lesions.

Although the incidence of both transient and permanent PoH was high in the control group as compared to the study group, there was no statistically significant difference (p>0.05) probably due to the small size of the study. However, an important observation was that in the control group, although all patients had normal serum calcium levels up to the day of discharge, one patient started developing biochemical hypocalcemia at the time of follow up on day 15 and this persisted up to 1 year despite calcium supplementation. But none of the patients in the study group developed biochemical hypocalcemia during hospital stay or during follow-up.

This finding reiterates the hypothesis that ischemic damage occurs to the parathyroid glands during dissection which is transient in most cases but can be permanent sometimes leading to permanent PoH. This complication can safely and easily be avoided by routine PTHAT of at least one parathyroid gland which gets revascularised over a period of time and prevents permanent PoH.