IDENTIFICATION OF AUTO-TRANSPLANTED PARATHYROID TISSUE BY TC-99M METHOXY ISOBUTYL ISONITRILE SCINTIGRAPHY

Parathyroid tissue is sometimes autotransplanted into the forearm afte r 'total' parathyroidectomy in patients with renal failure. Recurrent hyperparathyroidism demands identification of the source of PTH secret ion which cannot be assumed to be the forearm. To this end, Tc-99m met hoxy isobutyl isonitrile (MIBI) scintigraphy was used to identify func tioning auto-transplanted parathyroid tissue in seven patients undergo ing renal replacement therapy (five with functioning renal transplants and two on haemodialysis). Serum PTH was estimated in venous blood ta ken proximal and distal to the forearm graft and from the contralatera l arm, and subsequent Tc-99m MIBI scanning was carried out without kno wledge of the PTH results. Five patients had a significant gradient in PTH levels between sites proximal and distal to the graft, and betwee n the proximal site and the contralateral arm, suggesting functioning parathyroid tissue in the graft. Subsequent Tc-99m MIBI scintigraphy c onfirmed the activity of the autotransplanted parathyroid tissue in th ese five patients. In the remaining two patients without a significant PTH gradient between the sampling sites, Tc-99m MIBI scintigraphy did not identify any functioning forearm parathyroid tissue. The scan res ults therefore correlated well with the gradients in PTH levels, sugge sting that MIBI scintigraphy can be used to identify functioning auto- transplanted parathyroid tissue. The results also indicate that any pa tient who has undergone auto-transplantation of parathyroid tissue mus t have blood samples taken from veins proximal to the graft and either distal to it, or from the contralateral arm when parathyroid status i s re-assessed, particularly when surgery is being considered for recur rent hyperparathyroidism.