Motor neuron disease (MND) is a progressive condition that progressively damages parts of nervous system or degeneration of upper and lower motor neuron. This leads to muscle weakness, often with visible wasting
Motor function is controlled by the upper motor neurons in the brain that descend to the spinal cord; these neurons activate lower motor neurons. The lower motor neurons exit the spinal cord and directly activate muscles.
With no nerves to activate them, muscles gradually weaken and waste. Motor neuron disease (MND) can affect a person’s ability to walk, speak, swallow and breathe
DIFFERENT LEVELS OF THE NERVOUS SYSTEM ARE INVOLVED:-
- Frontal atrophy in the precentral gyrus
- The corticobulbar pathway
- The cranial nerve nuclei
- The corticospinal tract
- The anterior horn cell
THE MOTOR NEURON DISEASES MANIFESTS IN DIFFERENT FORMS LIKE-
- Amyotrophic lateral sclerosis
- Progressive muscular Atrophy
- Progressive bulbar palsy
- Primary lateral sclerosis
1)PROGRESSIVE MUSCULAR ATROPHY:-
- Male population are involved more at a ratio of 4:1.
- There is strictly lower motor neuron type of presentation beginning in the hands.
- There is gross weakness, wasting , in the hand and then the disease progresses to involve the other parts of the extremities as well as the lower limbs.
- In the lower limb peritibial muscles are involved-footdrop.
- Unlike ALS; this disease progresses very gradually up to 10 to 15 year and there are no signs of corticospinal tract involvement.
2) PROGRESSIVE BULBAR PALSY:-
Involvement of motor nuclei in the lower brainstem.
- There is a primary involvement of the bulbar muscles and hence the jaw muscles, facial muscles, tongue larynx and pharynx are affected.
- Due to involvement of the bulbar muscles the patient suffers from dysphagia, dysarthria etc.
- As the muscles of mastication and deglutition are affected the food particles get stuck to one corner of the mouth.
- Fibrillation of tongue is very common.
- Weakness of pharyngeal muscles causes improper pushing of food particles into esophagus giving rise to chocking.
- In later stage-UMNL and jaw jerk may be exaggerated giving rise to –strong blinking of eyes
- Wide opening of mouth(bull dog appearance)
- Death in this condition mainly due to –respiratory failure and the whole disease progresses within a span of 2 years.
3) PRIMARY LATERAL SCLEROSIS:-
It may also have hereditary predisposition and there is only UMN type of presentation.
- Only involvement of both the corticospinal and cortico bulbar
- It gives rise to UMN type of presentation in the extremities and face.
- No fasciculation
- Pathologically severe loss of pyramidal cells.
4) AMYOTROPHIC LATERAL SCLEROSIS(ALS):-(Lou Gehrig’s disease)
- It usually begins at around 40-50 years of age.
- Men are more affected and 5% cases are predisposed by hereditary.
- It exhibit mixed presentation =UMNL+LMNL
- thinning of anterior roots of spinal cord.
- Most noticeable in cervical and lumbosacral regions.
- Loss of neuron in motor cortex.
- Loss of neuron in cranial nerves, nuclei and anterior horns
- Section of brain stem : reduction of corticospinal fibres.
- No evidence of inflammatory response is seen in involved structure.
ALS is inherited in 5 to 10 percent of cases, while the rest have no known cause.
Researchers are studying several possible causes of ALS, including:
- Gene mutation. Various genetic mutations can lead to inherited ALS, which causes nearly the same symptoms as the noninherited form.
- Chemical imbalance. People with ALS generally have higher than normal levels of glutamate, a chemical messenger in the brain, around the nerve cells in their spinal fluid. Too much glutamate is known to be toxic to some nerve cells.
- Disorganized immune response. Sometimes a person’s immune system begins attacking some of his or her body’s own normal cells, which may lead to the death of nerve cells.
- Protein mishandling. Mishandled proteins within the nerve cells may lead to a gradual accumulation of abnormal forms of these proteins in the cells, destroying the nerve cells.
Possible environmental factors
Environmental factors may also play a role.
One study has reported that military personnel deployed in the Gulf region during the 1991 war were more likely to develop ALS than military personnel deployed elsewhere.
Some possible links have been found between ALS and exposure to:
- mechanical or electrical trauma
- military service
- high levels of exercise
- high levels of agricultural chemicals
- high levels of a variety of heavy metals
However, there is no conclusive evidence that specific lifestyle changes can decrease the risk.
- Limb-onset- a symmetric weakness and wasting of extremities-75%.
- Bulbar onset- bulbar or pseudobulbar features-25% dysphagic or dysarthria.
- In both limb –onset and bulbar-onset disease the key features is the mixture of upper and lower motor neuron involvement with normal sensation.
- FRONTAL LOBE INVOLVEMENT:- frontal dementia (3-5%) ,
- Emotional lability-unprovoked outbursts of laughing or crying occur.
- Limb-onset disease:- Limb onset ALS results from involvement of corticospinal tract and anterior horn cells.Involvement of corticospinal tract-
- Increase tone
- Brisk reflexes
- Extensor plantar responses
- Distinctive distribution of weakness
- Spasticity is rarely severe
- Anterior horn cell involvement leads to-
- Muscle atrophy
- Muscle cramps
- In the hand- wasting is evident-
- 1st dorsal interosseous muscle and tendon become prominent as hand muscles waste, giving ‘guttered’ appeareance- SKELETON HAND
- EMG reveals denervation with fibrillation
- Nerve conduction studies shows normal velocities and exclude in all limbs multi focal neuropathy with conduction block.
- MRI or myelography where appropriate excludes foramen magnum or spinal cord compression.
- Thyroid and calcium studies exclude endocrine or metabolic disease.
- In selected cases screen for paraproteinaemia,lymphoreticular disease and hexosaminidase deficiency.
Diagnostic criteria (E1 Escorial criteria for MND/ALS-world federation of neurology)
- LMN signs in at least 2 limbs
- UMN signs in at least 1 region on (bulbar/cervical/lumbosacras
- Progression of disease
- Sensory sign
- Neurogenic sphincter disturbance
- Other clinically evident CNS/PNS disease
- Exclusion of ALS like syndrome
Treatment is primarily that of managing symptoms and supporting both patient and family as these progresses and their heads change.
- Anartheria and dysarthria – speech assessement and communication aids when indicated.
- Dysphagia and aspiration- percutaneous endoscopic gastrostomy (PEG)
- Nutrition- estimate calorific content and supplement diet with vitamins
- Muscle weakness- physiotherapy, walking aids splint etc.
- Respiratory failure- as vital capacity drops respiratory failure becomes inevitable.
-Non-invasive ventilator assistance should be considered when this falls below 75% or orthophoea develop in patient without severe bulbar involvement.
Disease-modifying treatment :-
RILUZOLE is a drug with energy buffering and anti-glutamate properties.
#. It is the only approved treatment and in a dose of 100 mg daily is safe with a marginal effect in prolonging survival by 2 months.
To keep the patient as active as possible within the limits of pathology.
- Gentle active exercises should be given in order to maintain the range of motion and as well as to maintain the strength.
- Passive ROM and gentle stretching also help in maintaining the range as well maintain the circulation in the area.
(PROM) should be started only when the limb cannot be moved at all.
- Self-stretching is taught to the patient to get rid of the cramps which he is likely to get.
- No form of vigorous restricted exercise should be given as they give rise to increase fatiguability and cramps.
- The patient should be kept as mobile as possible through walking or standing for as long as possible.
To assist walking assistance by some relatives or attainder is sufficient, sometime the patient need a stick or tripod.
- Secondary complication in the form of pressure sores and contracters should be avoided and when the person goes into respiratory failure, chest physiotherapy become necessary.
- Vigorous chest physiotherapy techniques are generally avoided as they are too painful for the paitient.
Once the patient is on ventilator and needs clearance of airway the chest physiotherapy is administered little more vigorously.
- Light weight orthosis may be given for certain patient to gain stability at the joint that may help the patient in being functionally independent for alonger time.
- Proper positioning of the patient is necessary because once the limbs becomes increasing difficult to maintain the upright position.
- Psychological counseling is very essential to prevent the patient from going into a state of depression and to keep his motivation level high.