Factors correlated with hypermetabolism in patients with amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a severe disease characterized by neurogenic amyotrophy and degeneration of upper and lower motor neurons. Although ALS patients usually experience reductions in fat-free mass (FFM), hypermetabolism via an undetermined source has also been reported.

The objective was to clarify the metabolic level of ALS patients.

We measured the resting energy expenditure (REE) of 62 patients (32 men and 30 women) with ALS and investigated the factors correlated with metabolic level. Nutritional evaluation included bioelectrical impedance analysis, indirect calorimetry, and calculation of the body mass index. Neurologic assessment included an evaluation of peripheral and central neurologic deficit. Forced vital capacity was measured and smoking status was noted. A complete blood cell count was made and thyroid hormone and C-reactive protein concentrations were measured.

Patients were hypermetabolic, by an average of approximately 10% more than in a reference healthy population. FFM, age, and the neutrophil count were significantly associated with REE. The only variable that contributed to the prediction of REE, REE/Z100 kHz (bioimpedance at 100 kHz), REE adjusted for FFM, or the ratio of measured REE to calculated REE was the neutrophil count, which explained only a small percentage of variance in the multiple regression analysis. Hypermetabolism was not associated with a reduction in respiratory function, tobacco use, hyperthyroidism, spasticity and fasciculation intensities, or infection.

Our study corroborates the surprising finding that ALS patients are hypermetabolic. FFM, age, sex, manual muscular testing, the modified Norris limb score, weight, and an increase in circulating neutrophil counts correlated with the hypermetabolic state. Other factors may play a role in pathophysiologic processes that involve mitochondrial energy production or even sympathoadrenergic activation.