PBL 10 - Cerebral Palsy

• What is an upper motor neuron?

  Primary neurone found in the pyramidal tracts (corticospinal and corticobulbar) which synapses with a lower motor neurone found in the ventral horn of the spinal cord

  
• What is a lower motor neuron?

  Secondary neurone found in the pyramidal tracts which synapses with skeletal muscle 2 types:Alpha motor neurone - synapses with extrafusal muscle fibres Gamma motor neurone - synapses with intramural muscle fibres of skeletal muscle spindles

  
• What is a neurone lesion?

  Damage or injury to a nerve which disrupts its normal function
• How do upper and lower motor neurone lesions differ?

  LMN lesion shows no activity of EMG whereas UMN lesion presents as numerous peaks

  
• What is paralysis? What are its 2 forms?

  = A condition of muscle weakness caused by nerve damage or disease - typified by a weakness of voluntary movement, or by partial loss of voluntary movement or by impaired movement- Spastic paralysis = a condition in which the muscles affected are marked by tonic spasm and increased tendon reflexes- Flaccid paralysis - in which muscle tone is lacking in the affected muscles and in which tendon reflexes are decreased or absent.
• What is muscle tone?

  Muscle tone is the amount of tension (or resistance to movement) in muscles at rest. Our muscle tone helps us to hold our bodies upright when we are sitting and standing - muscles contract slightly to stabilise joints and bones - this is elicited by the stretch reflex
• How does voluntary contraction of a muscle affect muscle tone?

  When you actively use muscles, the force generated by muscle contraction is much higher than the normal muscle tone due to the inc activation of the alpha motor neurone by the excitatory fibres of the CST
• What is hypertonia?

  A condition in which there is too much muscle tone - arms or legs are stiff and hard to move. Caused by an UMN lesion 3 types...
• What are the 3 types of hypertonia? Give an example of when each is seen

  Spastic hypertonia (spasticity) - seen in spastic CP due to loss of inhibition by the CST as well a MS, strokes etc. Dystonia - involuntary muscle contractions that cause abnormal movements or postures often due to damage to basal ganglia - seen in dyskinetic CP . Rigidity - muscle stiffness of both agonist and antagonist which is independent of movement of muscle - resists movement - often caused by imbalances in NTs in brain
• What is cerebral palsy?

  A non-progressive disorder of movement and posture that appears during infancy or early childhood (before the age of 5) resulting from damage to the brain causing an upper motor neurone lesionIt consists of many different subtypes
• What are the different areas of the brain that are typically affected?What type of CP does each result in?

  cerebral cortex --> spastic CP (70% cases)

  basal ganglia --> dyskinetic CP (athetoid or dystonic)

  cerebellum --> ataxic CP

  multiple areas --> mixed CP

  
• What is responsible for the range in severity seen in CP?

  The extent of the damage and location
• What is the most common type of CP?

  Spastic
• What is spastic CP characterised by?

  Disorder of the stretch reflex UMN lesion --> injury to the inhibitory fibres of the corticospinal tract --> net disinhibition of spinal stretch reflexes --> inc excitation of extrafusal muscle fibres via alpha motor neurone at rest (inhibitory fibres of CST usually prevent this)
• What is the purpose of the stretch reflex?

  To maintain basal muscle tone to allow for axial and appendicular control against gravity to maintain postureCST utilises this reflex to elicit voluntary movement by inc excitation of the alpha motor neurones
• What different types of nerves do muscle spindles have?

  Type 1a and 2 afferents as well as alpha and gamma motor neurones (LMN)

  
• Describe the stretch reflex which occurs when muscles stretch

  1. Stretch of muscle stretches spindle embedded within Type 1a and 2 afferents tightly wrap around spindle and depolarise when stretched2. Inc stretching leads to inc firing of APs towards spinal cord3. Type 1 afferents synapse with alpha motor neurons of the leg extensors and cause these muscles to contract which prevents damage from overstretching4. Type 2 afferents synapse with inhibitory interneurones which inhibit the alpha motor neurons of the leg flexor muscles causing them to relaxLeg kicks out BUT this causes spindle to shorten and become slack, causing the spindle afferents to cease firing - now insensitive to muscle strteching...bad!So..type 1a afferents also synspase with gamma efferents which innervate intrafusal muscle fibre of the spindle preventing this

  
• How is the stretch reflex regulated?

  CST possesses both excitatory and inhibitory fibresAt rest, inhibitory fibres synapse with alpha motor neurone of reflex arc and reduce excitation Under voluntary control, excitatory fibres of the CST are triggered which override this and excite the alpha motor neurone --> exaggerated stretch reflex and contraction

  
• What does spastic CP result in?

  hypertonia and spasticity - positive signs of a UMN lesion
• How does spastic cerebral palsy result in hypertonia?

  Injury to the inhibitory fibres of the CST --> exaggeration of stretch reflex --> inc tone of the extrafusal muscle fibres, particularly in antigravity muscles (flexors)
• Why is hypertonia worse in flexor muscles in spastic CP?

  These muscles work against gravity Gravity results in inc stretch of these compared to extensors --> inc stretch reflexNormally this is good as allows for postural control BUT in CP, dec inhibition by the CST --> exaggeration of the stretch reflex --> inc tone
• What is spasticity characterised by?

  Inc contraction/tone of muscle as stretched due to inc firing of type 1a and 2 afferents --> inc excitation of already excited alpha motor neurone
• How does spastic cerebral palsy result in hyperreflexia?

  Hypertonia of the flexors --> inc stretching of extensors --> inc stretch of spindle --> inc firing of type 1a and 2 afferents = inc sensitivity so faster reflex
• What are the different types of spastic CP?

  hemiplegic - 1 hemisphere of motor cortex damaged --> effects on contralateral side diplegic - both hemispheres of the motor cortex are affected BUT mainly legs of the homunculus quadriplegic - both hemispheres of the motor cortex are affected

  
• What are some clinical signs of CP?

  Affects the contralateral side, with a greater impact on the upper limb Hypertonia and spasticity of the antigravity muscles results in:- Exaggerated plantar flexion of foot --> circumductive gait - Exaggerated flexion of arm and wrist - Weakening of hand and foot dorsiflexors due to reduced usage - Unilateral clonus of ankle - prolonged hypertonia can result in spasms of the antigravity muscles - Babinski sign
• When can CP develop?

  Before, during or after birth
• How can CP develop before birth?

  - Periventricular leukomalacia - caused by a lack of blood/oxygen --> death of white matter surrounding the ventricles - CST runs through this area- Infection caught during pregnancy - such as cytomegalovirus, rubella, chickenpox- Stroke - this can be hemorrhagic (IVH) or ischaemic
• What is PVL? Why are premature infants at risk of this?

  Where the white matter (leuko) surrounding the ventricles of the brain (periventricular) is deprived of blood and oxygen leading to softening (malacia)Premature infants often have delicate bvs in their brain which can be damaged easily by infection, inflammation etc —> lack of blood flow and O2 to certain areas of the brain —> PVL --> UMN lesions

  
• What is an IVH and why is it a risk factor for the development of CP?

  Intraventricular hemorrhage (IVH)This is a haemorrhage occurring with the space of the ventricles which will disrupt the CST that runs through here --> CP
• How can CP develop during birth?

  Asphyxiation causing a lack of oxygen --> damageThis can occur during a difficult birth
• How can CP develop after birth?

  - CNS infection such a meningitis --> inflammation and damage- Serious head injury- Choking or drowning leading to a lack of oxygen to the brain- Hypoglycaemia- Stroke
• What are some external risk factors?

  - Being born prematurely- Having a low birthweight- Being part of a multiple birth - higher risk of a complicated birth- Mother smoking, drinking excessive alcohol or taking explicit drugs doing pregnancy
• Can we prevent CP?

  NOBut there are several preventative methods to reduce the risk or identify it earlier
• What are some physical consequences of spastic CP?

  Hypertonia and spasticity result in:- Contractures (shortening of muscles due to prolonged contraction) - Scoliosis- Drooling - due to poor oromotor control of tongue, lips and facial muscles (NOT inc production)- Osteoporosis (thinning of trabecular bone) due to constant remodelling of bone due to alternate loading of the joints
• How does spastic hemiplegic CP affect gait?

  Spastic cerebral palsy results in hypertonia and spasticity of the flexors --> stiff, awkward movements Spastic hemiplegic CP affects the contralateral side of the body --> fixed plantar flexion of the foot etc This results in the acquisition of a circumductive gait due to the patient not being able to perform the initial heel strike of the gait cycle, nor dorsiflex their foot during the midswing This causes the patient to compensate --> swinging of the foot around rather than upwards

  
• What gait can spastic diplegic CP result in?

  Scissor gait

  
• If spastic CP affects the upper motor neurones, how do changes to sensation occur?

  Both the pre-central and post-central gyri share the same blood supply: middle cerebral arteryThus any problems involving this vessel will affect both the primary motor and somatosensory cortices

  
• What sensory deficits can be be seen in spastic CP?

  Damage to the primary somatosensory cortex and association areas can result in agnosia, astereognosis and a negative 2-point touch discrimination etc
• What is astereognosis?

  = inability to identify an object by active touch of the hands without other sensory input, such as visual or sensory information.
• Which drugs can be used to manage hypertonia and spasticity seen in spastic CP?

  Diazepam, baclofen and botox