Hydration in Amyotrophic Lateral Sclerosis

Abstract

Water is essential for health and survival. Water needed for health exceeds the amount the body produces through metabolic activity. Although water intake is predominantly as free water or in liquid drinks, about a quarter comes from solid foods such as meats and vegetables. Water exists as total body water (TBW) that constantly replenishes and occurs in intracellular and extracellular compartments. Recommended daily water intake is 3.0 L in men and 2.5 L in women and decreases with normal aging; inadequate intake in healthy elderly results in increased morbidity and mortality. Amyotrophic lateral sclerosis (ALS), a neurodegenerative disease of middle age, causes diffuse weakness with dysfunction in the limbs and bulbar muscles accompanied by erosion of quality of life and early death from respiratory failure. Although often discussed in ALS circles, the assessment and management of dehydration are frequently overlooked. Dehydration assessed by the gold standard-labeled water method to examine daily water turnover, a surrogate for water intake, occurs in 20% of ALS patients at first evaluation; its degree increases as the disease progresses. TBW and water turnover are 1,200 ml (3.4%) and 260 ml/day (8.6%) lower, respectively, in ALS patients compared to age- and gender-matched healthy controls. Risk factors for poor hydration are female gender, bulbar-onset disease, malnutrition estimated by body mass index, and low lung function measured by incentive spirometry. As in the healthy elderly population, decreased water intake adversely affects survival in ALS patients. Equations used to estimate daily water requirement, recommended by the US Centers for Medicare and Medicaid Services in healthy elderly, are inaccurate for use in ALS patients. Validated equations are now available to accurately estimate hydration using endpoints routinely assessed in ALS clinics. As with nutrition, hydration should be regularly examined at ALS clinic visits using these equations to assess water requirements and improve clinical care.