Lecture 30 Myogenic palsies

Question 1

What is myasthenia gravis?

what muscles are effected?

Answer 1

autoimmune condition
arises from severely weak muscle

*Only striated muscle affected
*effects all of the striated muscle or affects only some specific groups.
Order of frequency is:
*extra ocular, facial, bulbar, neck, limb, girdle, distal limb and trunk.
*Inter costal (respiratory) muscles are affected the disease may prove fatal

Question 2

Does myasthenia gravis effect females or males more?

Answer 2

• Ages 20-30: females>males
• Ages 50-60: males>females

Question 3

What is the aetiology of MG in paeds?

Answer 3

1.Neonatal
-born to myasthenic mother
-disease is self-limiting (6 weeks approx.)
2.Congenital
-infants born to non-myasthenic mothers
3. uvenile
-Develops in infancy
-More spontaneous remissions than adults

Question 4

What is the aetiology of MG in adults?

Answer 4

1. Ocular myasthenia
   -Limited to eye muscles
   -If still limited to muscles after 2 years, highly unlikely to become generalised
2. Mild to moderate (generalised)
   -Often slow onset of symptoms
   -Doesn’t effect respiratory muscles
3. Acute fulminating (generalised)
   -Rapid onset
   -Early involvement of respiratory muscles
4. Late severe (generalised)
   -Severe
   -Develops 2 years after first signs of muscle weakness
5. Drug related
   -D-Pencillamine induced myasthenia
   -This drug is used in rheumatoid arthritis, systemic lupus

Question 5

Why are the muscles weak in MG?

Answer 5

-MG px develop antibodies to the receptor sites at the muscle end plate
-antibodies prevent Ach from binding and this reduces neurotransmitter take-up
-Ack continues to be released until supply is exhausted and muscle fatigues

Question 6

What are the systemic symptoms and signs of MG?

Answer 6

General
*Fatigue
*Lack of energy
Limb girdle
*Difficulty getting out of a chair
*Difficulty climbing stairs
Facial
*Lack of facial expression
Bulbar
*Problems with speech
Respiratory
*Problems breathing

Question 7

What are the ocular signs and symptoms of MG?

Answer 7

Ptosis
*marks onset of disease in 70% of cases

Diplopia
*marks onset of disease in 70% of cases

Orbicularis weakness
*ask them to close eyes and scrunch up lids tight.
*Gently try to pen up there eye. This will be easily done in these px.

Question 8

Describe the ptosis you will get in someone with MG?

Answer 8

*Usually bilateral
*Often asymmetrical
*Increases with fatigue (px may say lids get lower throughout the day)
*Frontalis over-action seen to elevate eye (scrunching forward)
*Occasional lid retraction in attempt to elevate the more ptoic eye

Question 9

What must you ask to investigate ptosis?

How can you check if the ptosis is due to MG?

Answer 9

does it vary across the day?

*Request px to elevate their eyes for 1-2 minutes and look at pen torch
*If Severity of ptosis increases after this in PP, suspect MG

-ice pack test: ice pack is placed on both eyelids for 2 minutes.
-if ptosis improves-strong indication of ptosis

Question 10

What is cogan’s lid twich?

Answer 10

*Request patient to depress their eyes for 15 seconds and then look in PP
*Lid movement follows eyes movement on depression
*The lid initially moves above its previous level when eyes return to PP
*Lid then returns to its original ptotic position.

Question 11

What is Gorelick’s sign?

Answer 11

*Done when px has asymmetric ptosis
*Examiner holds up the more ptotic lid
*Innervational drive to both eyes is reduced
*Ptosis on the less affected side starts to increase

Question 12

How can you investigate diplopia in MG?

Answer 12

does double vision vary across the day?

*Variable diplopia (horizontal to vertical)
*Diplopia increases as muscles fatigue
*Mimics any type of muscle palsy (L-R palsy now IR palsy)
*May mimic internuclear ophthalmoplegia (INO)
*May mimic gaze palsy

Question 13

How can you check for orbicularis weakeness?

Answer 13

• Can usually close eyes
• May not be able to bury eye lashes
• Unable to stop examiner opening eyes with gentle pressure

Question 14

When must you suspect MG?

Answer 14

*Ocular symptoms increase with fatigue
*Systemic symptoms increase with fatigue
*Diurnal variation symptoms worse as the day progresses
*Weakness increases after exercise
*In the earlier stages the weakness maybe intermittent

VARIABILITY IN SYMPTOMS

Question 15

How can you detect MG?

Answer 15

-receptor antibodies (detected in bloodtest)
-enlarged thymus gland
-tensilon test (short-acting anticholinesterase is injected)

Question 16

What disease is associated with MG?

Answer 16

thyroid eye disease (5%)

Question 17

What is the systemic treatment of MG?
what is the ocular treatment of MG?

Answer 17

*Longer acting anticholinesterases pyridostigmine (mestinon)
*Immunosuppressive agents such as systemic steroids
*Plasmaphoresis to reduce level of circulating antibody or intravenous immunoglobulin
*Thymectomy (20%-60% of patients can enter remission)

Ocular treatment of Myasthenia Gravis
Ptosis props.
* Contact lens
Occlusion
* Blenderm on glasses
* Frosted lens
* Occlusive contact lens
Surgery
* Contraindicated unless stable for a long time

Question 18

What is lambert-eaton rooke syndrome (LERS)?

what disease is it associated with?

when does risk reduce?
why should you monitor closely for first 2 years?

Answer 18

*Defect is presynaptic.
*Proximal limb weakness

*Association with small cell carcinoma

• After having LERS for 2 years, risk reduces
• Monitored closely for first 2 years for cancer

Question 19

What are the characteristics of LERS?

Answer 19

*Limb weakness
*The muscles resting action potential is reduced
*Muscles action potential increases after repetitive stimulation
*Dry mouth
*Ptosis in approximately 50% of cases
*Extraocular muscle involvement very unusual
*Response to tensilon is unpredictable.

Question 20

What is the management of LERS?

Answer 20

-exclude malignancy
-guanidine hydrochloride
-ptosis props

Question 21

What are the characteristics of chronic progressive external ophthalmoplegia?

Answer 21

*Progressive symmetrical loss of ocular motility
*Progressive symmetrical bilateral ptosis
*Loss of Bell’s reflex (i.e. eyes don’t roll upwards when lids are closed)
*If the loss is not symmetrical, px may not complain of diplopia
*Orbicularis weakness
*Pupillary responses normal as smooth muscle not affected
-end stage: eyes are severely mechanically restricted “FROZEN EYE”

Question 22

What is the aetiology of CPEO?

Answer 22

*It is the commonest of the mitochondrial myopathies.
*CPEO is often associated with Kearne-Sayre-Daroff syndrome.

Kearne-Sayre-Daroff syndrome (Features):
* Onset before 20 years old.
* Fine pigmentary retinopathy
* Heart conduction block

Question 23

What is the management of CPEO?

Answer 23

If complains of diplopia:
* Prisms
* Occlusion
* Occlusive contact lens
* Blenderm
* Frosted glasses
Surgery if eye is grossly eccentrically fixated.

Question 24

What are the characteristics of orbital myositis?

Answer 24

*Inflammation of one or more of the extra-ocular muscles
*Usually unilateral
*Occasionally bilateral
*Proptosis. Measured using an exophthalmometer.
*Pain
*Lid oedema
*photphobia
*Conjunctivitis with or without chemosis

*limitation of extra-ocular movements:
-Paretic in direction of muscle action
-Mechanical in the opposite direction

Question 25

What is the aetiology of orbital myositis?

what is the dd?

what is the management?

Answer 25

-autoimmune disorders

*orbital cellulitis
*orbital abscess
*hematoma
*Grave’s disease (thyroid eye disease)
*Tumours

-systemic steroids

Question 26

What is Rhabdomyosarcoma?

what are the signs?

what is the management?

Answer 26

*Highly malignant tumour of the striated muscle
*60 children/year in the UK
*70% occur during first decade (boys >girls)

*May present with a tropia in early stages
*Limitation of eye movement in early stages
*Rapid (weeks) tumour growth will lead to proptosis

-rapid diagnosis and treatment
-radiotherapy and chemotherapy