15.5.4 Weakness

Question 1

Define Weakness

Answer 1

• Weakness is a decreased ability to voluntary and actively move muscles against resistance
• Weakness may arise from any portion of the motor unit and is typically divided into upper motor neuron and lower motor neuron weakness.

Question 2

Upper motor neuron weakness

Answer 2

• UMN weakness arises from lesions in the cerebral cortex and corticospinal tracts down to, but not including the anterior horns cells in the ventral spinal cord

Question 3

Lower motor neuron weakness

Answer 3

LMN weakness results from lesions located in the anterior horn cell, peripheral nerve , neuromuscular junction, or muscle.

Question 4

NB Upper vs Lower motor neuron signs

Answer 4

Lower
- floppy weak
- tongue fasiculation’s
- tendon reflexes likely to be reduced absent
- alert; gross and fine motor delay
- low pitched progressively weaker cry
- weakness in anti-gravitational limb muscles
- Arthrogryposis +++ (child born with deformities)

Upper
- floppy strong
-
- Tendon reflexes increased Clonus, Babinski’s +
- Higher function likely to be affected. Seizures. Global developmental delay
-
- Axial weakness a significant feature
- Arthrogryposis

Question 5

Evaluation: Clinical clues from history

Answer 5

• Antenatally : Quality of fetal movements, Breach presentation Oligo or polyhydramnios
• Evidence to support perinatal asphyxia (HIE)
• Arthrogryposis multiplex congenita
• Onset of the hypotonia from birth (congenital) or acquired.
• Familial consanguinity
• Mother: Myasthenia / early cataract surgery / myotonia (shake her hand)

Question 6

Muscle examinations

Answer 6

Inspection: Muscle atrophy versus muscle hypertrophy/fasciculations/ptosis Palpation and percussion: Muscle tenderness

Tone: Test positions/180 degree flip (supine to prone)

Muscle strength: MRC grading system in older child

Pattern of muscle weakness: Generalized/symmetrical versus asymmetrical/ Symmetrical weakness divided into proximal/distal or regional weakness

Question 7

Muscle inspection

Answer 7

Muscle atrophy - Denervation or chronic muscle disuse
Muscle hypertrophy - Duchene muscular dystrophy
Tongue fasciculations - Anterior horn cell SMA
Ptosis - Myasthenia Gravis Botulism Neurotoxic Snake bite envenomation

Question 8

Central Hypotonia = Floppy strong

Answer 8

• pader willi syndrome
• Zellweger syndrome

Question 9

LMN = Floppy weak

Answer 9

Which compartment?
- anterior horn cell SMA
- dorsal nerve root
- peripheral nerve
- neuromuscular junction
- muscle

Question 10

Spinal muscular atrophy

Answer 10

• Apoptosis of anterior horn cells in SMA infant
• Inheritance: autosomal inheritance (1/4 chance to have affected child)

Clinical features
- Facial expression and attentiveness are good.
- Weakness symmetrical; proximal more than distal; legs more affected than arms Poor head control
- Typical “frog-like” posture
- Weakness of the intercostals with relative sparing of the diaphragm
- Bell shaped chest & paradoxical breathing pattern
- Tongue fasciculation’s
- Bulbar weakness, difficulty swallowing, risk of aspiration
- Cranial nerves spared
- Cognition is normal, with bright alert facies
- Deep tendon reflexes absent

Classification
1. Symtomatic <6 months; no sitting
2. Sit but never walk
3. Walking

Question 11

Useful indicators of weakness

Answer 11

• Ability to cough and clear airway secretions (“ cough test”)
• Swallowing function
• The character of the cry
• Paradoxical breathing pattern
• Frog-like posture and quality of spontaneous movements.

Question 12

Charcot Marie Tooth Disease

Answer 12

• Irrespective whether the myelin or axon is affected, axonal degeneration results, and correlates with severity of weakness.
• The axonal degeneration affects the longest fibers first, and hence symptoms Usually begin distally and in the lower limbs first.

Classification
- Neurophysiological and histopathological characteristics together
with mode of inheritance and phenotypical clues is used to quide genetic testing.
- The number of genetic disorders causing CMT is growing.
- Phenotypic and genotypic cross over between various CMT types

Clinical features
- Age of onset may vary, most often first two decades of life
- Severity of the disease may vary greatly
- Gait disturbance: high stepping gait, difficulties running, frequent falls
- Foot deformity: hammer toes and pes cavus
- Upper limbs: atrophy of the hand muscles (claw hand)
- Symmetrical atrophy of the peroneal muscles, later involving the calves and eventually the lower third of the thigh. (stork like/inverted champagne bottles)
- Deep tendon reflexes, especially ankle reflexes are often lost early. - Sensory abnormalities are mild and may be difficult to elicit.
- Abnormalities of touch, propioception and vibration, sensory ataxia. Pain and touch sensation is not impaired.
- Vasomotor disturbances are common, with freq cyanosis and marbling of the skin.

Question 13

Duchenne muscular dystrophy

Answer 13

• lack or cannot or produce dystropin
• Becker is almost the same; just a later disease and less severe
• Heart can also become weak
• walk on toes (compensatory mechanism)
• short test any boy baby who is not walking within 18 months should be tested for this
• inheritance: X-linked recessive (can do prenatal testing)
• cardiac surveillance (make sure heart doesn’t get weak)
• resp care (BiPAP - breathing support at night)

Clinical manifestations
- Delay in passing milestones. Difficulty in climbing stairs.
- Difficulty in arising from the floor.
- Speech delay (less than 10 words by 2 years of age)
- Any boy not walking by 18 months.
- Gower sign. Lumbar lordosis. Waddling gait.
- Pseudohypertrophy of the calves (due to fat and collagen proliferation)
- Symmetrical progressive proximal muscle weakness.
- Loss of ambulation 10 years.
- Progressive decrease of deep tendon reflexes.
- Cardiac involvement.
- Scoliosis
Intellectual impairment.