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General introduction | 9

Motor neuron disease

Motor neuron diseases (MNDs) are fatal diseases that lead to loss of upper and lower
motor neurons and can affect all voluntary muscles, and include amyotrophic lateral
1,2
sclerosis (ALS), progressive muscular atrophy (PMA) and primary lateral sclerosis (PLS).
The presentation of symptoms and the rate of disease progression varies greatly between 1
MND’s. ALS is the most prevalent and aggressive MND, affecting both the upper and lower
motor neurons, with an average survival of 2 to 4 years from disease onset. However some
patients may survive for more than 10 years. In patients with PMA only the lower motor
neurons are affected, and the average survival is 5 years from disease onset, while PLS only
affects the upper motor neurons and is not fatal in most cases. In a subgroup of patients,
PMA and PLS can develop into ALS, generally within the first years after diagnosis. 3–9

The initial symptoms of MND’s may occur in the arms or legs, known as a spinal onset, or
show in difficulties with speech and swallowing, known as a bulbar onset. As the disease
progresses, patients will experience progressive loss of motor function, which inhibits
daily activities, such as walking, writing, getting dressed and eating. Symptoms generally
1,2
start focal (in one body part), and will spread to other parts of the body. Besides physical
impairments, cognitive impairments and psychological issues, such as frontotemporal
dementia and feelings of hopelessness, are also common in patients with MND. 10,11 Over
time, patients with MND will develop respiratory muscle weakness, which will lead to
respiratory failure, and consequently, death in most patients. 12,13 Out of all respiratory
muscles, weakness of the diaphragm is the main cause of respiratory impairment, as it
inhibits adequate inhalation, and leads to shortness of breath (dyspnea). During sleep,
diaphragm weakness will lead to nocturnal hypoventilation, resulting in abnormally high
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carbon dioxide levels in the blood, known as hypercapnia. Patients with prolonged
hypercapnia may experience sleep-related complaints (e.g. restless sleep, nightmares,
morning headaches) and daytime symptoms (e.g. excessive fatigue, daytime sleepiness),
which can cause distress and negatively affect quality of life. 15,16

Multidisciplinary care

As a result of the complexity and heterogeneity of MND, patients require specialized care
at a multidisciplinary ALS clinic, provided by a team consisting of at least a neurologist,
(rehabilitation) physician, physical therapist, occupational therapist, speech and language
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therapist, dietician and psychologist. Due to disease progression, patients are generally
monitored every 3 months during a visit to a multidisciplinary clinic. In the Netherlands
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there are 25 certified multidisciplinary ALS clinics spread across the country, but in most
countries the density of specialist centers is lower. In between clinic visits, care at home is