Influence of Olfacto-gustatory Sensoriality on the Nutritional Status of Patients With Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterised by progressive diffuse muscular paralysis due to the inexorable loss of motor neurons in the primary motor cortex, the corticospinal tract, the brain stem and the spinal cord.

Over the course of the disease, when the phrenic motor neurons are involved, diaphragmatic weakness develops, leading to restrictive respiratory failure, which is the main cause of morbidity and mortality. Non-invasive ventilation (NIV) compensates for diaphragm failure and corrects the associated symptoms, and has been shown to prolong patient survival and improve quality of life.

Undernutrition is another recognised prognostic factor. Several mechanisms have been described, foremost of which are a state of hypermetabolism and a reduction in food intake secondary to chewing difficulties, dysphagia, a loss of dexterity in the upper limbs, a disturbance in salivary secretion or psychological disorders. In addition, diaphragmatic dysfunction plays a direct role in the onset of undernutrition, as compensatory contraction of the accessory neck muscles increases resting energy expenditure.

However, the hedonic sensations triggered by a meal play a role in controlling food intake beyond the simple energy balance between calorie intake and energy expenditure. Olfacto-gustatory sensoriality could therefore play a role in the nutritional status of patients suffering from ALS.

Diaphragmatic dysfunction may also influence nutritional status by other mechanisms. For example, the reduction in inspiratory capacity associated with diaphragmatic insufficiency reduces olfaction in a group of tetraplegic patients. Central sensory impairment could exacerbate this phenomenon. Although it is conventionally considered that there are no sensory manifestations during the course of ALS, minor but diffuse abnormalities of the nerves and sensory action potentials have been observed. A central alteration in olfacto-gustatory sensoriality could be part of the neurological manifestations of ALS. In addition, olfactory deficits occur in other neuromuscular diseases with central involvement, such as myasthenia, Parkinson's or Alzheimer's disease, in the absence of concomitant cognitive or diaphragmatic impairment.

Our hypothesis is that impaired olfacto-gustatory function favours the onset of undernutrition in ALS.

Current nutritional management consists of ensuring adequate calorie intake by prescribing oral food supplements or inserting a gastrostomy. Taking personalised account of food preferences during dietary advice or of a potential olfacto-gustatory deficit, by reinforcing smells or tastes during food consumption, would be an interesting additional therapeutic avenue for improving patients' nutritional status, quality of life and prognosis