Motor neuron disease (MND) is a disorder of anterior horn cells, resulting in weakness of muscles in myotomal pattern. Motor neuron disease is of various types such as infectious (poliomyelitis), familial (amyotrophic lateral sclerosis) sporadic (primary lateral sclerosis or primary muscular atrophy). Here is given an interesting account of this set of neurological disorders.
1. Causes of MND:
Following factors have been postulated to be precipitating the motor neuron disease:
Mutation of the cytosolic Cu/Zn superoxide dismutase gene located on chromosome 21 has been found to be causing 20 % of the familial amyotrophic lateral sclerosis (ALS) and 2 % of the total cases of ALS.
Glutamate is an excitatory neurotransmitter, over stimulation of glutamate receptors lead to neuronal degeneration in anterior horn cells.
C. Oxidative Stress:
Oxidative stress in the form of free radicals makes significant contribution towards development of motor neuron disease.
D. Miscellaneous Factors:
Vascular endothelial growth factor dysregulation, mitochondrial dysfunction, protein aggregation in motor neuron and neuroinflammation mediated by non-neuronal cells may also play a part.
2. Important Statistics:
Important statistics about about MND include:
1-3 people per 100000 are affected by MND.
B. Mean Age of Onset:
Mean age of onset is 55 years.
C. Gender Predisposition:
MND is more common among males with a male to female ratio of 3:2 and 10% of the total cases are of familial origin.
D. Types of MND:
The most common type of MND occuring is amyotrophic lateral sclerosis (ALS), which expresses itself in the form of both upper motor neuron and lower motor neuron signs. Primary lateral sclerosis (PLS) with its purely upper motor neuron signs and progressive muscular atrophy (PMA) with its purely lower motor neuron signs are just 2 ends of the spectrum of ALS.
3. Symptoms of MND:
Following can be the symptoms of MND:
A. Muscle Weakness:
Progressive muscle weakness is the hallmark and most often the presenting symptom of MND.
Muscle twitching or fasciculations is an important symptom of MND. These can also be associated with muscle cramps and body fatigue.
C. Bulbar Symptoms:
Bulbar involvement in MND can lead to dysarthria, dysphagia, dysphonia, difficulty with coughing and chewing eventually leading to sialorrhoea. Tongue fasciculations can be observed in these cases but tongue should never be looked for fasciculations when protruding because in this position many such abnormalities can be picked, which actually are not present.
D. Fatal Consequences of Muscle Weakness:
Dysphagia eventually leads to weight loss and and respiratory muscle weakness ensues respiratory problems.