Guillain-Barre syndrome and SIADH

The syndrome of inappropriate secretion of antidiuretic hormone (SIADH) in Guillain-Barré syndrome (GBS) is a very often overlooked entity even though it is well-described. However, most of the previous observations are case reports. There are no systematic studies of SIADH in GBS.

To assess the incidence and characteristics of SIADH in patients with GBS and to assess whether it is a predictor of poor outcome.

We prospectively studied 50 patients with GBS admitted to the Department of Neurology in a tertiary care hospital in South India from January 2009 to April 2010. After obtaining clinical history, electrophysiologic studies were performed to determine the GBS subtype. SIADH was diagnosed based on modified Bartter and Schwartz criteria.

SIADH was detected in 24 of the 50 patients (48%) at some stage of the illness (median 8.8 days after GBS onset). Six of them had mild SIADH, 12 patients had moderate SIADH, and 6 patients had severe SIADH. MRC sumscore at the time of admission and discharge was higher in patients with SIADH (p < 0.001) when compared to the normal group. Bulbar weakness and need for ventilatory support were higher in GBS with SIADH (13 vs 1, p < 0.001). Mean duration of hospitalization was longer in SIADH (29.15 vs 10.57, p < 0.001). Most of the patients with GBS with SIADH required plasmapheresis (23 vs 8, p < 0.001). There are 4 variables significantly associated with mortality, which include age >50, ventilatory support, hyponatremia, and bulbar weakness.

SIADH is a common and important electrolyte disorder encountered in GBS. It has significant association with severity of GBS and is an indicator of poor prognosis. It can be symptomatic even though the majority of patients are asymptomatic.