4.2: Defects in the sensory system

Question 1

Define the following terms 
A) hyperasthesia
B) hyperalgesia
C) Paraesthesia 
D) Dysaesthesia 
E) Allodynia

Answer 1

A) Increased sensitivity to any stimulus
B) Increased sensitivity to a painful stimulus
C) Pins and needles/burning sensation
D) Inappropriate sensation to a stimulus
E) pain provoked by a non painful stimulus

Question 2

Describe the kind of pain that may be felt in a peripheral nerve lesion

Answer 2

Borders are well demarcated and may involve hyperasthesia, discomfort or pain

Question 3

Describe how pain may present in a nerve root lesion

Answer 3

Sensory loss might be more vague but generally in dermatomal distribution, not anesthesia due to overlap of dermatomes. Pain may radiate

Question 4

Describe how a spinal cord lesion may present

Answer 4

Mix of motor and sensory signs/symptoms

Question 5

Name two examples of vascular nerve damage

Answer 5

Diabetes and peripheral vascular disease

Question 6

How might peripheral nerve damage present?

Answer 6

1. Distal symmetrical neuropathy
2. Multifocal neuropathy
3. Mononeuropathy

Question 7

What is a multifocal neuropathy and what is a mononeuropathy?

Answer 7

Multifocal neuropathy: Focal areas of multiple motor nerves are attacked by the immune system

Mononeuropathy: single peripheral nerve (transmitting messages from brain to peripheral body is damaged)

Question 8

What is multifocal neuropathy characterized by?

Answer 8

Progressive, asymmetrical muscle weakness and atrophy

Question 9

Define the timelines for an acute, subacute and chronic peripheral nerve disease

Answer 9

Acute: <4 wks
Subchronic: 1-6 months
Chronic: >6 months

Question 10

How might you investigate an individual with potential peripheral nerve damage?

Answer 10

1. Nerve conduction studies; stimulates specific nerves and records their ability to send impulses to the muscle
2. CSF
3. Biochemistry; toxins

Question 11

Names one example of a toxin which may accumulate and cause neuropathies

Answer 11

Renal failure may cause a buildup of urea

Question 12

What causes distal symmetrical neuropathy in diabetes and what vital mechanism of the body does this hinder?

Answer 12

Damage to the blood supply to peripheral nerve endings, making them hypoxic and hypersensitive; causes sensory symptoms such as numbness and painful paraesthesia

Damage to the finer sensing nerves loses the feedback mechanism of pain, predisposing diabetes to infections, ulcers, etc

Question 13

How many diabetes will experience neurophysiological signs after 10 years?

Answer 13

Nearly 100%

Question 14

What is the most common cause of neuropathy in the developed world?

Answer 14

Diabetes

Question 15

Why are amputations more commonly be performed in diabetics?

Answer 15

The vascular damage means the damage/infection has poor blood supply, and often cannot resolve despite antibiotics

Question 16

What does GB syndrome predominantly affect and what is the classic presentation?

Answer 16

Motor nerves, classically presents with ascending paralysis that ranges from mild weakness-complete paralysis

Question 17

How many patients with GB syndrome require respiratory support? How is recovery and what is the mortality rate?

Answer 17

~20% require respiratory support

Recovery is spontaneous usually after a few weeks, mortality rate is 5%

Question 18

How is GB syndrome managed and why?

Answer 18

Plasma exchange: because many people with GBS will have had a recent chest/respiratory infection which they’ve developed antibodies which are subsequently attacking the nerves - plasma exchange may remove soluble factors, including these antibodies

IV immunoglobulin: made from donated blood containing healthy antibodies

Question 19

Name four toxins which may cause a peripheral neuropathy

Answer 19

Lead, arsenic, mercury, ethanol

Question 20

Name an infection which may cause a peripheral neuropathy

Answer 20

Leprosy

Question 21

Name three nutritional factors which may cause a peripheral neuropathy

Answer 21

Deficiencies in thiamine, B12, niacin

Question 22

Where would niacin be found and what can it cause?

Answer 22

Certain legumes, may cause the 3 Ds: diarrhea, dementia and dermatitis

Question 23

How does a B12 deficiency affect the nervous system? How is a B12 deficiency (And pernicious anemia) treated?

Answer 23

Damages the myelin sheath that surrounds and protects nerves, can give hydroxycobalamin

Question 24

Name five systemic diseases that can cause peripheral neuropathies

Answer 24

Diabetes, cancer, sarcoidosis, uraemia, HIV/AIDS

Question 25

Name four medications that can cause peripheral neuropathies

Answer 25

Amiodarone (anti-arrhythmic), cis-platinum (chemo), isoniazid (antibiotic), and vincristine (chemo)

Question 26

What causes brown-sequard syndrome and how does it present?

Answer 26

Hemisection of spinal cord (incomplete spinal injury) with hemiparaplegia on one side and hemianaesthesia on the other side

Question 27

What happens below the lesion in brown-sequard syndrome and which spinal tracts are involved?

Answer 27

1. Ipsilateral Upper motor neurone weakness - corticospinal tracts are affected which may leads to spastic paralysis, brisk reflexes and upgoing plantars
2. Ipsilateral loss of proprioception and vibration - dorsal columns
3. Contralateral loss of pain and temperature - lateral spinothalamic tract

Question 28

Name four potential causes for brown-sequard syndrome

Answer 28

MS, trauma, tumour, disk degeneration

Question 29

What causes a subacute combined degeneration of the spinal cord and what is the onset?

Which afferent sensory pathway is damaged and which is always preserved?

Answer 29

B12 deficiency, slow onset. Causes symmetrical dorsal column loss but even in severe cases the spinothalamic tracts are preserved (don’t know why)

Question 30

Where is B12 stored in the body and how long does storage last before depletion occurs?

Answer 30

Liver, 4 years

Question 31

Where is B12 metabolized and absorbed in the body?

Answer 31

Metabolized (along with intrinsic factor from stomach lining cells) in the stomach and absorbed (carried by intrinsic factor) in the ileum

Question 32

Name five conditions associated with B12 deficiency (not including pernicious anemia)

Answer 32

“My diet can make problems”

1. Megaloblastic anemia: insufficient amount and abnormally large RBCs
2. Mental slowing
3. Dorsal columns affected
4. Cerebellar ataxia
5. Peripheral neuropathy

Question 33

Other than a B12 deficiency, what can cause pernicious anemia?

Answer 33

Autoantibodies against intrinsic factor or parietal cells

Question 34

Describe the pathology of syringomyelia, which ascending sensory tract is damaged?

Answer 34

There is a progressive expansion of the central fluid cavity/canal in the spinal cord which destroys the white matter and the spinothalamic tract as its fibres cross segmentally near the centre of the spinal cord.

Question 35

Which regions of the spinal cord and which regions of the body are commonly affected by syringomyelia?

Answer 35

Spine: Commonly the lower cervical/upper thoracic
Body: upper limbs (‘cape-like’ distribution)

Question 36

What are four potential causes for syringomyelia?

Answer 36

Congenital, trauma, idiopathic, tumour

Question 37

Describe the sensation loss and pain that occurs in a thalamic brain lesion, name one disease where this occurs

Answer 37

Sensation: loss/impairment of all forms of sensation on the contralateral side
Can lead to chronic pain, such as in degerine-Roussy syndrome (thalamic stroke)

Question 38

Describe the sensational changes that occurs in a sensory cortex brain lesion

Answer 38

Contralateral sensory changes

Impaired sensory recognition
-asterognosis: inability to identify common objects on manual examination

-two point touch discrimination damaged which is more marked in the hands

Question 39

Name the two pathologies which give rise to “glove and stocking” sensory loss

Answer 39

Demyelination and axonal degeneration

Question 40

What rare lesion affects the dorsal roots and columns and is a late symptom of syphilis?

Answer 40

Tabes dorsalis

Question 41

What is sensory ataxia?

Answer 41

Movement disorder arising from the loss of sensory input necessary for motor feedback

Question 42

What is a positive Romberg sign and with what lesions would it be seen?

Answer 42

Inability to stand with feet together and eyes closed without swaying

Present in conditions causing sensory ataxia, such as lesions to the dorsal column tract

Question 43

What is sensory agnosia?

Answer 43

Loss of ability to recognize objects, faces, places or voices

Question 44

Your patient walks with difficulty picking his feet up and stamping them down in a “stick and stamp” pattern of gate, can you suggest what’s wrong with him? His serum B12 is very low

What condition is this symptom associated with?

Answer 44

1. Prolonged B12 deficiency causes degenerative changes in the dorsal columns
2. This leads to sensory agnosia, which in turn reduces pressure and touch sensations from the limbs - causing a loss of position sense
3. This sensory deficit causes patients to not feel their feet properly or be unsure if their feet or in touch with the ground when they walk - so to maximize their sensory input they looks at their feet and stamp down as they walk

Associated with subacute combined degeneration of the spinal cord

Question 45

Why is sensory loss bilateral in syringomyelia?

Answer 45

Because lesions in syringomyelia are in the central spinal cord (enlargement of the central cavity), and thus impinge on both sides of the spinothalamic cord

Question 46

What symptoms (including sensory) are you likely to experience in syringomyelia?

Answer 46

Bilateral sensory loss: loss of sensation in hands, temperature loss

Disturbances in the ANS