Motor Neuron Diseases

 Lower classification of Motor Neuron Diseases


Diseases of the lower motor neurons caused by nerve cells in the brainstem and spinal cord. Lower motor neurons control movement in the arms, legs, chest, face, throat, and tongue.

Diseases - all described below - include:

Progressive bulbar palsy  also called progressive bulbar atrophy

Progressive muscular atrophy

Spinal muscular atrophy SMA

SMA type I, also called Werdnig-Hoffmann disease

SMA type II

SMA type III (Kugelberg-Welander disease)

Fazio-Londe disease

Kennedy disease, also known as progressive spinobulbar muscular atrophy

Congenital SMA with arthrogryposis

Progressive bulbar palsy also called progressive bulbar atrophy, involves the bulb-shaped brainstem - the region that controls lower motor neurons needed for swallowing, speaking, chewing, and other functions.  Symptoms include pharyngeal muscle weakness, weak jaw and facial muscles, progressive loss of speech, and tongue muscle atrophy.  Limb weakness with both lower and upper motor neuron signs is almost always evident but less prominent.  Affected persons have outbursts of laughing or crying (called emotional lability).  Individuals eventually become unable to eat or speak and are at increased risk of choking and aspiration pneumonia, which is caused by the passage of liquids and food through the vocal folds and into the lower airways and lungs.  Stroke and myasthenia gravis each have certain symptoms that are similar to those of progressive bulbar palsy and must be ruled out prior to diagnosing this disorder.  In about 25 percent of ALS patients early symptoms begin with bulbar involvement.  Some 75 percent of patients with classic ALS eventually show some bulbar involvement.  Many clinicians believe that progressive bulbar palsy by itself, without evidence of abnormalities in the arms or legs, is extremely rare.

Progressive muscular atrophy is marked by slow but progressive degeneration of only the lower motor neurons.  It largely affects men, with onset earlier than in other MNDs.  Weakness is typically seen first in the hands and then spreads into the lower body, where it can be severe.  Other symptoms may include muscle wasting, clumsy hand movements, fasciculations, and muscle cramps.  The trunk muscles and respiration may become affected.  Exposure to cold can worsen symptoms.  The disease develops into ALS in many patients.

Spinal muscular atrophy SMA is a hereditary disease affecting the lower motor neurons.  Weakness and wasting of the skeletal muscles is caused by progressive degeneration of the anterior horn cells of the spinal cord.  This weakness is often more severe in the legs than in the arms.  SMA has various forms, with different ages of onset, patterns of inheritance, and severity and progression of symptoms.  Some of the more common SMAs are described below. 

SMA type I, also called Werdnig-Hoffmann disease , is evident by the time a child is 6 months old.  Symptoms may include hypotonia (severely reduced muscle tone), diminished limb movements, lack of tendon reflexes, fasciculations, tremors, swallowing and feeding difficulties, and impaired breathing.  Some children also develop scoliosis (curvature of the spine) or other skeletal abnormalities.  Affected children never sit or stand and the vast majority usually die of respiratory failure before the age of 2.

Symptoms of SMA type II usually begin after the child is 6 months of age.  Features may include inability to stand or walk, respiratory problems, hypotonia, decreased or absent tendon reflexes, and fasciculations.  These children may learn to sit but do not stand.  Life expectancy varies, and some patients live into adolescence or later.

Symptoms of SMA type III (Kugelberg-Welander disease) appear between 2 and 17 years of age and include abnormal gait; difficulty running, climbing steps, or rising from a chair; and a fine tremor of the fingers.  The lower extremities are most often affected.  Complications include scoliosis and joint contractures-chronic shortening of muscles or tendons around joints, caused by abnormal muscle tone and weakness, which prevents the joints from moving freely.

Symptoms of Fazio-Londe disease appear between 1 and 12 years of age and may include facial weakness, dysphagia (difficulty swallowing), stridor (a high-pitched respiratory sound often associated with acute blockage of the larynx), difficulty speaking (dysarthria), and paralysis of the eye muscles (ophthalmoplegia).  Most patients die from breathing complications.

Kennedy disease

also known as progressive spinobulbar muscular atrophy , is an X-linked recessive disease.  Daughters of patients with Kennedy disease are carriers and have a 50 percent chance of having a son affected with the disease.  Onset occurs between 15 and 60 years of age.  Symptoms include weakness of the facial and tongue muscles, hand tremor, muscle cramps, dysphagia, dysarthria, and gynecomastia (excessive development of male breasts and mammary glands).  Weakness usually begins in the pelvis before spreading to the limbs.  Some patients develop noninsulin-dependent diabetes mellitus.  The course of the disorder varies but is generally slowly progressive.  Individuals tend to remain ambulatory until late in the disease.  The life expectancy for individuals with Kennedy disease is usually normal. Factsheet from MND Vic

Congenital SMA with arthrogryposis (persistent contracture of joints with fixed abnormal posture of the limb) is a rare disorder.  Manifestations include severe contractures, scoliosis, chest deformity, respiratory problems, micrognathia (unusually small jaws), and ptosis (drooping of upper eyelids).

lower motor neuron

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