ABSTRACT
Background & objectives: Plasma and urinary metanephrines are used as screening tests for the diagnosis of phaeochromocytoma. The recommended cut-off levels are not standardized. This study was conducted to identify a cut-off level for 24 h urinary fractionated metanephrines viz. metanephrine (uMN) and normetanephrine (uNMN) using enzyme immunoassay for the diagnosis of phaeochromocytoma. Methods: Consecutive patients suspected to have phaeochromocytoma were included in the study. uMN and uNMN in 24 h urinary sample were measured using a commercial ELISA kit. Results: Overall, 72 patients were included over a period of 18 months. Twenty patients had histopathologically confirmed phaeochromocytoma and in 52 patients phaeochromocytoma was ruled out. Using the upper limit of normal stated by the assay manufacturer as the cut-off, uMN >350 μg/day had a low sensitivity and uNMN >600 μg/day had a poor specificity. By increasing the cut-off value of uNMN to twice the upper limit, specificity increased significantly without much loss in sensitivity. Combining uMN and uNMN using a cut-off twice the upper limit improved the diagnostic performance - sensitivity (95%); specificity (92.3%); positive predictive value (PPV - 82.6%); negative predictive value (NPV - 98%). In subsets of patients with a variable pretest probability for phaeochromocytoma, the PPV correlates well with the occurred of these tumors decreased, while the NPV remained at 100 per cent. Interpretation & conclusions: ELISA is a simple and reliable method for measuring uMN and uNMN. The test has a good NPV and can be used as an initial screening test for ruling out phaeochromocytoma. Each hospital will have to define the cut-off value for the assay being used, choosing a proper control population.
ABSTRACT
BACKGROUND: Hypokalaemic periodic paralysis constitutes a heterogeneous group of disorders that present with acute muscular weakness. In this analysis, we discuss the aetiological factors that appear to be more common in the Indian population. METHODS: From 1995 to 2001, 31 patients presented with periodic paralysis (mean age 34.5 years, range 11-68 years). Of the 31 patients, 19 were men. The clinical and laboratory data of these patients were analysed. Patients were investigated for possible secondary causes of hypokalaemla. RESULTS: There were 13 patients (42%) with renal tubular acidosis, 13 with primary hyperaldosteronism (42%), 2 each with thyrotoxic periodic paralysis and sporadic periodic paralysis, and I with Gitelman syndrome. Of the 13 patients with renal tubular acidosis, 10 had proximal and 3 distal renal tubular acidosis. Three of these patients with renal tubular acidosis had Sjogren syndrome. The patients diagnosed to have renal tubular acidosis had significantly lower serum bicarbonate (18.7 [14.6] v. 29.6 [5.0] mEq/L; p < 0.05) and higher levels of chloride (107.5 [6.0] v. 99.5 [3.4] mEq/L; p < 0.05) compared with those who had primary hyperaldosteronism, although the potassium values were similar (2.4 [0.65] v. 2.26 [0.48] mEq/L; p = 0.43). All patients with primary hyperaldosteronism had hypertension at presentation and were proven to have adrenal adenomas. CONCLUSION: A significant number of patients in this study had secondary and potentially reversible causes of hypokalaemic periodic paralysis. The common causes were renal tubular acidosis and primary hyperaldosteronism. A detailed work-up for secondary causes should be undertaken in Indian patients with hypokalaemic periodic paralysis.