Differential diagnosis neuro v mech

Question 1

Neurogenic palsies

Answer 1

IIIrd, IVth, VIth, all may be unilateral or bilateral and individual muscle palsies

Question 2

Mechanical palsies

Answer 2

Blow out, Brown’s, Duanes, CFEOM, Graves orbitopathy, Retinal detachment, Tumours, Myositis

Question 3

Investigation

Answer 3

Testing deviations in neurogenic palsies- Size of deviation in p.p. is dependant on extent of palsy.

Question 4

Ocular movements

Answer 4

Neurogenic - Maximum limitation is in the position of the main action of the affected muscle. The amount of movement is greater on duction than version unless a complete paralysis

Mechanical- Restriction is usually in the opposite direction to the affected muscle & is across the field of action e.g. Blow out # restriction in elevation. Duction & version movements are equally limited

Question 5

Deviations

Answer 5

Neurogenic- Size of deviation in p.p. is dependant on extent of palsy.

Mechanical- In many cases despite a large restriction of movement the deviation in p.p. is very small

Question 6

HESS

Answer 6

Neurogenic- Field of affected eye smaller with proportional spacing between inner & outer fields. Both fields are displaced according to the deviation.

Mechanical- Field of affected eye smaller with inner & outer fields being close together.

Question 7

IOP

Answer 7

Neurogenic- Unchanged in all gaze positions.

Mechanical- Raised when looking away from the site of the lesion.

Question 8

FDT

Answer 8

Neurogenic- Full passive movement unless secondary muscle contracture has occurred.

Mechanical- Limited passive movement generally in the opposite direction to the lesion, sometimes in the same direction or both directions.

Question 9

Diplopia

Answer 9

Neurogenic- Except in IIIrd nerve & bilateral IVth the direction of diplopia remains the same e.g. R/L

Mechanical- Diplopia often reverses e.g. R/L in elevation L/R in depression

Question 10

Head posture

Answer 10

Neurogenic- A combination head posture is common in neurogenic vertical muscle palsies
Mechanical- Just head up / down common in mechanical restrictions

Question 11

Pain

Answer 11

Neurogenic- No pain on movement
Mechanical- Pain in acquired lesions and some cases of Brown’s syndrome

Question 12

Muscle sequelae

Answer 12

Neurogenic- Full muscle sequelae esp. if longstanding
Mechanical- o/a of contralateral synergist only

Question 13

Saccades

Answer 13

Neurogenic- Slowed in the direction of u/a
Mechanical- Normal movement comes to an abrupt end

Question 14

Glove

Answer 14

Neurogenic- No change in globe position .
Mechanical- Retraction of the globe when the eye is turned in the direction opposite to the restriction. DUANES

Question 15

FDT

Answer 15

Neurogenic-…
Mechanical- positive FDT
https://www.youtube.com/watch?v=ntnYaF1KUEg

Question 16

FDT method

Answer 16

Either as OPD procedure with local or during surgery under GA
Fixation forceps, two pairs used at opposite limbal points. The globe is then rotated horizontally, vertically and obliquely. Ensure lift as well as rotate.
Gauge the degree of limited movement and amount of resistance (requires experience)
Indenting of globe indicates tight conjunctiva
Cotton bud if forceps too uncomfortable
Get pt to look in direction required place bud at limbus and try to increase range of movement. Ensure don’t press down on globe

Question 17

Muscle function tests

Answer 17

FDT
Muscle force generation (4 techniques)
Spring back balance test
Muscle stetch est
Exaggerated FDT
Electromyopgraphy

Question 18

Muscle force generation (4 techniques)
A

Answer 18

Method A
* The pt is instructed to look away from the field of action of muscle under investigation
* Cotton tip bud placed firmly over muscle insertion
* Pt asked to look in position of gaze of muscle action
* No or little movement of the eye = paralysis
* Pressure felt on the bud but able to prevent movement = moderate paresis
* Examiner cannot prevent eye movement = mild paresis or normal function

Question 19

Muscle force generation (4 techniques)
B

Answer 19

Method B
* Stabilise the eye with toothed forceps
* Instruct pt to move eye against this obstacle
* Determine if can feel a tug on the forceps & how much (experience required)

Question 20

Muscle force generation (4 techniques)
C

Answer 20

As above but a moving pointer is attached to the toothed forceps

Question 21

Muscle force generation (4 techniques)
D

Answer 21

• A suction cup with a strain gauge fitted to a contact lens and applied to the eye and held by a handle
• Strain gauge registers force exerted on attempted movement

Question 22

Spring back test

Answer 22

During surgery the surgeon can passively rotate the eye using forceps at the limbus. Then the remove the forceps and observe if the eye springs back in to pp or remains eccentric. Then they can rotate the eye in the opposite direction and release to make smaller observations. Then this is repeated several times

Question 23

Muscle stretch test

Answer 23

During surgery the muscle is detached and drawn forwards. If normal it should be possible to advance its insertion to the centre of the cornea with the eye in p.p. Less than this indicates stiffness of the muscle

Question 24

Exaggerated FDT

Answer 24

Assess tendon laxity in superior oblique palsy:

Grip the limbal conjunctiva firmly at specific clock positions (4 o’clock and 10 o’clock for the right eye, 2 o’clock and 8 o’clock for the left eye).
Retropulse and rotate the eye upwards and nasally. Normal tendon will mildly restrict movement, which increases with tightness and decreases with laxity.
Assess tendon tension by moving the eye nasally to temporally; a ‘bump’ should be felt with a normal tendon. Absence of the ‘bump’ suggests laxity or tenotomy.
If laxity is suspected, excyclorotate the eye and repeat the tests for further evaluation.

Question 25

Electromyography EMG

Answer 25

It includes using a topical anaestheic and fine electrodes inserted into the muscle. Patient is asked to look into direction of limitation and then the opposite. Many patients aren’t suitable for this test.

Question 26

EMG in neurogenic

Answer 26

partial or complete loss of motor unit activity

Question 27

EMG in mechanical

Answer 27

increased activity when attempts to look in direction of limitation

Question 28

EMG in myopathies

Answer 28

may be decreased activity during contraction of affected muscle

Question 29

Importance of differential diagnosis

Answer 29

Differential diagnosis is important because it may determine further investigations requires. Also, it affects management in particular surgical correction of the deviation.