Prueba de calcitriol en el diagnóstico diferencial del hiperparatiroidismo / Test with Calcitriol in the Differential Diagnosis of Hyperparathyroidism

El hiperparatiroidismo primario (HPP) clásico presenta hipercalcemia y PTH elevada. Actualmente, se describen formas atípicas con calcemia y/o PTH normal. El calcitriol inhibe la secreción de PTH en ausencia de autonomía. Para evaluarla, realizamos una prueba de inhibición con calcitriol en 103 pacientes con elevación mínima, intermitente o ausente de calcio iónico (CaI), calcio total (CaT) y/o PTH. Se midió CaT, CaI y PTH séricos, y calcio/creatinina urinaria de 24 y 2 horas previo y posterior a la administración oral de 0,75 ug de calcitriol por 10 días. Se excluyeron aquellos con 25OHD menor a 20 ng/ml y/o seguimiento inferior a un año. La respuesta se clasificó en dos grupos: A) hipercalcemia con PTH alta o normal (HPP) o B) descenso de PTH sin aumentar la calcemia (hiperparatiroidismo secundario). El HPP fue confirmado por imágenes y/o cirugía. Ambos grupos fueron similares en edad y 25OHD, con un seguimiento promedio de 70 ± 34 meses. El CaT y CaI basales y pos prueba fueron significativamente mayores en el grupo A que en el B, donde se mantuvieron estables. La calciuria se incrementó en ambos grupos por igual, en forma dependiente (grupo A) e independiente (grupo B) de la calcemia. La PTH basal fue similar en ambos grupos. Posprueba, se produjo un descenso significativamente mayor en el grupo B (44 % ± 18) que en el A (15 % ± 27), sugiriendo resistencia al calcitriol. Con curvas ROC, una inhibición menor al 30 % posee una sensibilidad (S) y especificidad (E) de 85 % y 88 % para el diagnóstico de HPP. Dos pacientes del grupo B desarrollaron HPP clásico a los 17 y 37 meses de seguimiento lo que otorga a la prueba una S 90 % y E 100 % para el diagnóstico de HPP, constituyendo una herramienta útil y rápida para evidenciar la autonomía paratiroidea.

Primary hyperparathyroidism (PHP) is a disorder characterized traditionally by hypercalcemia and elevated levels of parathyroid hormone (PTH). However, this complete biological pattern is sometimes lacking. Some PHP patients display either normal or intermit tently elevated serum calcium level as well as hypercalcemia with normal PTH levels. PTH synthesis is negatively controlled by calcitriol through the vitamin D receptor (VDR). We assessed the diagnostic value of a PTH inhibition test with calcitriol in the diagnosis of PHP, in 103 patients who have minimal, intermittent, or no elevation of the levels of total or ionized calcium, and/or intact PTH. Patients with 25OHD < 20 ng/ml or less than a year follow up were excluded. We measured serum total calcium (CaT), ionized calcium (CaI), PTH and urinary calcium in 47 patients before and after the oral administration of calcitriol 0.75 ug once daily for 10 days. The biochemical response was classified as A) increase in serum calcium with high or normal PTH levels (PHP) or B) PTH suppression without hypercalcemia (secondary hyperparathyroidism). PHP was confirmed by images or surgery. The two groups were similar in age and 25 OHD levels. The mean follow up was 70 ± 34 months. Basal serum CaT and CaI were higher in group A. After the loading, this difference was even bigger, what gives additional specificity to the measure. Urine calcium was equally augmented by calcitriol in both groups, with coincident elevation of serum calcium in group A but not in B, in which serum calcium remained stable. Basal PTH levels were similar in both groups, so they cannot reliable distinguish between both types of hyperparathyroidism. After the calcitriol load, PTH dropped 44 % ± 18 in group B versus 15 % ± 27 in group A, suggesting some degree of resistance to the hormone action in PHP. ROC curves shows that a reduction of less than 30 % in PTH levels can diagnose PHP with 85% sensibility and 88% specificity. Only two patients in group B behaved as PHP at 17 and 37 months follow up, what gives the test 90 % sensibility and 100 % specificity for the diagnosis of PHP. So, this well-tolerated and easily performed test could be used for the diagnosis of PHP in patients suspected for the disease despite the normality of some basal biological markers.

False positive in the measurement of thyroglobulin induced by rheumatoid factor.

BACKGROUND: We report a case of interference in thyroglobulin (Tg) measurement in a woman with differentiated thyroid cancer and rheumatoid arthritis history. Due to discordant Tg in relation to TSH concentrations and negative images, we investigated possible interference in the measurement of Tg. METHODS: During the follow-up we measured Tg by chemiluminescence (TgQL) using Immulite 2000 immunoassay system. To investigate possible interference in Tg measurement, we made serial dilutions, re-testing of Tg by an alternative method: electrochemiluminescence, Cobas 6000 analyzer (TgEQL), recovery test of Tg and polyethylene glycol (PEG) 6000 precipitation. RESULTS: During the patient follow-up, the TgQL ranged between <0.3 and 16.1ng/ml. In the evaluated serum samples very high titers of rheumatoid factor (RF) were found. When RF titers were lowered post PEG precipitation, Tg QL concentrations became undetectable. CONCLUSION: We describe an unusual case of interference in Tg assay due to RF. When disagreement among Tg concentrations, images and clinical features is observed, we suggest taking into account the evaluation of possible Tg interference to avoid unnecessary complementary exams and inappropriate treatment.

Properties of musculus gluteus maximus in above-knee amputees.

The present study aimed at evaluating possible changes of the gluteus maximus muscle bulk size and in the contracting properties of gluteus maximus in the amputated above-knee limb. Seven male above-knee amputees, with a mean age of 47.4 years volunteered to participate in the present study. Twenty-one healthy subjects with a mean age of 34.0 years served as the control group. Muscle belly displacement was measured by means of a precision electromagnetic sensor dc-dc displacement transducer while performing maximal voluntary isometric contractions. The muscle twitch contraction has been quantified by the latency period (T1), time to peak tension (T2) and the slope of the record. A statistically significant decrease in muscle belly displacement on the amputated side has been observed in comparison with controls and non-amputated side. The latency period on the amputated side was significantly longer and the slope less steep than in the control group. These results indicated atrophied and slower gluteus maximus on the amputated side of above-knee amputees.