One can have difficulty breathing with climbing stairs (exertion), difficulty breathing when lying down (orthopnea), or even respiratory failure if breathing muscles become involved. Bulbar symptoms, including difficulty speaking (dysarthria), difficulty swallowing (dysphagia), and excessive saliva production (sialorrhea), can also occur. Sensation, or the ability to feel, is typically not affected. Emotional disturbance (e.g. pseudobulbar affect) and cognitive and behavioural changes (e.g. problems in word fluency, decision-making, and memory) are also seen. There can be lower motor neuron findings (e.g. muscle wasting, muscle twitching), upper motor neuron findings (e.g. brisk reflexes, Babinski reflex, Hoffmans reflex, increased muscle tone), or both.Motor neuron diseases are seen both in children and adults. Those that affect children tend to be inherited or familial, and their symptoms are either present at birth or appear before learning to walk. Those that affect adults tend to appear after age 40. The clinical course depends on the specific disease, but most progress or worsen over the course of months. Some are fatal (e.g. ALS), while others are not (e.g. PLS). Patterns of weakness
Various patterns of muscle weakness occur in different motor neuron diseases. Weakness can be symmetric or asymmetric, and it can occur in body parts that are distal, proximal, or both. According to Statland et al., there are three main weakness patterns that are seen in motor neuron diseases, which are:
Asymmetric distal weakness without sensory loss (e.g. ALS, PLS, PMA, MMA)
Symmetric weakness without sensory loss (e.g. PMA, PLS)
Symmetric focal midline proximal weakness (neck, trunk, bulbar involvement; e.g.
Both motor neurons are necessary for the strong contraction of a muscle, but damage to an UMN can be distinguished from damage to a LMN by physical exam. Tests
Cerebrospinal fluid (CSF) tests: Analysis of the fluid from around the brain and spinal cord could reveal signs of an infection or inflammation. Magnetic resonance imaging (MRI): An MRI of the brain and spinal cord is recommended in patients with UMN signs and symptoms to explore other causes, such as a tumor, inflammation, or lack of blood supply (stroke). Electromyogram (EMG) & nerve conduction study (NCS): The EMG, which evaluates muscle function, and NCS, which evaluates nerve function, are performed together in patients with LMN signs. For patients with MND affecting the LMNs, the EMG will show evidence of: (1) acute denervation, which is ongoing as motor neurons degenerate, and (2) chronic denervation and reinnervation of the muscle, as the remaining motor neurons attempt to fill in for lost motor neurons. By contrast, the NCS in these patients is usually normal. It can show a low compound muscle action potential (CMAP), which results from the loss of motor neurons, but the sensory neurons should remain unaffected. Tissue biopsy: Taking a small sample of a muscle or nerve may be necessary if the EMG/NCS is not specific enough to rule out other causes of progressive muscle weakness, but it is rarely used. Treatment
There are no known curative treatments for the majority of motor neuron disorders. Please refer to the articles on individual disorders for more details.