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 sharply demarcated so identifying cause should be simple

Pain may involve hyperasthesia, discomfort or pain

Question 3

Describe how pain may present in a nerve root lesion

How would pain NOT present in a nerve root lesion and why?

Answer 3

Sensory loss might be more vague but generally in dermatomal distribution. Pain may radiate

NOT anaesthesia due to overlap of dermatomes.

Question 4

Describe how a spinal cord lesion may present

Answer 4

Mix of motor and sensory signs/symptoms

Question 5

Name 3 examples of how peripheral nerves may be damaged/affected?

Which one of these can occur as a result of diabetes and peripheral vascular disease?

Answer 5

1) Axonal degeneration – toxic, metabolic, physical
2) Demyelination
3) Vascular nerve damage (diabetes and peripheral vascular disease)

Question 6

How might peripheral nerve damage present?

Give an example of a condition for each

Answer 6

1) Distal symmetrical neuropathy (diabetes)
2) Multifocal neuropathy (MS)
3) Mononeuropathy (MS)

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?

Give an example of a condition when each is used

Answer 10

1) Nerve conduction studies; uses 2 electrodes to stimulate specific nerves and records their ability to send impulses to the muscle (eg. used in really bad carpal tunnel syndrome)
2) CSF (eg. MS)
3) Biochemistry; looking for toxins (eg. in renal failure we are looking for a build up of urea)

Question 11

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

Answer 11

Damage to the small BV’s at the peripheries that supply the peripheral nerve endings, causes them to become hypoxic and hypersensitive. This leads to sensory symptoms such as numbness and painful paraesthesia

Damage to the finer sensing nerves causes loss of the feedback mechanism of pain. This causes neuropathy which can subsequently lead to ulcers, joints, skin infections etc

Question 12

List 2 things that should be recommended to a patient with diabetes

Answer 12

1) glycemic control

2) weight loss and exercise (especially type II)

Question 13

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

What marker can we use to monitor this condition?

Answer 13

Diabetes

Marker: HBA1C

Question 14

Why are amputations more commonly be performed in diabetics?

Answer 14

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

Question 15

What nerves does guillain barre predominantly affect + what is the classic presentation?

Answer 15

Motor nerves

Classically presents with ascending paralysis that ranges from mild weakness-complete paralysis

Question 16

How many patients with guillain barre require respiratory support?

How is recovery and what is the mortality rate?

Answer 16

~20% require respiratory support

Recovery is spontaneous usually after a few weeks,

Mortality rate is 5%

Question 17

How is guillain barre syndrome managed and why?

Answer 17

Management is supportive

Plasma exchange: antibodies developed against respiratory infections may also target the nerves. Hence plasma exchange may remove these antibodies

IV immunoglobulin: made from donated blood containing healthy antibodies

Question 18

Name four toxins which may cause a peripheral neuropathy

Answer 18

Lead, arsenic, mercury, ethanol

Question 19

Name an infection which may cause a peripheral neuropathy

Answer 19

Leprosy

Question 20

Name three nutritional deficiencies which may cause a peripheral neuropathy

Answer 20

Deficiencies in Thiamine, B12, niacin

Question 21

Give some examples of foods containing niacin

What can a deficiency cause?

Answer 21

peas, broccoli, potatoes, mango avocado

Deficiency: 3Ds: diarrhea, dementia and dermatitis

Question 22

How does a B12 deficiency affect the nervous system and how would you treat?

Why are B12 deficiencies commonly seen in patients who have had gastric bypass surgery?

Answer 22

Damages the myelin sheath that surrounds and protects nerves. Treat by giving hydroxycobalamin (B12)

Bypassing the stomach or terminal ilium means there will no B12 absorption or intrinsic factor function.

Question 23

Name four medications that can cause peripheral neuropathies and state what each is

Answer 23

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

Question 24

Name 4 systemic diseases that can cause peripheral neuropathies

Answer 24

1) Diabetes
2) cancer
3) sarcoidosis
4) uraemia
5) HIV/AIDS

Question 25

What is carpel tunnel syndrome?

Answer 25

Compression of the median nerve at the wrist

Question 26

Give 4 causes of carpal tunnel syndrome

Answer 26

1) Pregnancy
2) obesity
3) hypothyroidism
4) OA,
5) trauma
6) diabetes
7) acromegaly

Question 27

Give 2 signs of carpel tunnel syndrome

Answer 27

1) Sensory changes

2) Muscles wasting and weakness

Question 28

What 2 tests can be used to diagnose carpal tunnel syndrome?

Answer 28

Tinels: tap test
Phalen: stretch test

Nerve conduction studies can also be used to diagnose

Question 29

Give 3 treatments for Carpal tunnel syndrome

Answer 29

1) splints, stretching (& weight loss)
2) steroid injections
3) surgical decompression

Question 30

What is Meralgia paresthetica? (Hint: CK syndrome)

How would patient present?

Give 4 causes

Answer 30

Nerve entrapment of the lateral femoral cutaneous nerve

Presentation: numbness and burning on the outer area of the thigh

Causes: Pregnancy, trauma, tight clothing, diabetes

Question 31

Shingles is caused by reactivation of the ______ virus, which also causes the disease ______ when it initially infects people, usually in childhood.

The virus can lie dormant for many years within cell bodies of ______ located in the ______ ganglia.

It uses ______ transport to takes virus molecules towards cell body, and ______ transport to to travel away from cell body to affected skin sites. Shingles presents as a band-like painful rash that follows _________

It is commonly seen in _______ patients and is usually treated with ________ (a topical capsaicin)

Answer 31

Varicella Zoster, chicken pox, peripheral nerves, dorsal root

Retrograde, Anterograde, dermatomal distribution

Immunocompromised, Aciclovir

Question 32

What is Brown-Sequard syndrome?

Answer 32

Hemisection of the cord (rare)
characterised by a lesion in the spinal cord which results in weakness or paralysis (hemiparaplegia) on one side of the body and a loss of sensation (hemianesthesia) on the opposite side

Question 33

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

Answer 33

1) Ipsilateral upper motor neurone weakness - corticospinal tracts are affected which leads to spastic paralysis, brisk reflexes and up going plantars (b/c LMN behave abnormally)
2) Ipsilateral loss of proprioception and vibration - dorsal columns
3) Contralateral loss of pain and temperature - lateral spinothalamic tract

Question 34

Give 4 potential causes of Brown-sequard syndrome

Answer 34

MS, trauma, tumour, disk degeneration

Question 35

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

How does this present?

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

Answer 35

B12 deficiency with slow onset. Presents with increasing unsteadiness and numbness of extremities

Causes peripheral neuropathy due to symmetrical dorsal column loss

BUT even in severe cases the spinothalamic tracts are preserved (unknown why)

Question 36

Give 4 conditions caused by B12 deficiency

Answer 36

1) Megaloblastic anaemia
2) Mental slowing
3) Dorsal columns affected
4) Cerebellar ataxia
5) Peripheral neuropathy

Question 37

Where is Vit B12 metabolised and absorbed?

Answer 37

Metabolised in the stomach with intrinsic factor and absorbed in the ileum

Question 38

What causes Pernicious anaemia and how would you treat?

Answer 38

Autoantibodies to parietal cells or intrinsic factor

Treatment: hydroxycobalamin

Question 39

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

Answer 39

A cyst or cavity known as a syrinx forms within the spinal cord. This causes progressive expansion of the central fluid cavity of the spinal cord which destroys the white matter of the spinothalamic tracts, sparing the dorsal columns

It usually occurs in the lower cervical/upper thoracic region and is described as a classic ‘cape-like’ distribution. Hence there is usually upper limb dysfunction

May present with loss of sensation in hands and a subtle bilateral pain and temperature loss (early sign)

Cranial nerves may be damaged and which can be indicated in clinical presentation

Question 40

Describe the sensation loss and pain that occurs in a Thalamic brain lesion

Name one disease where this occurs

Answer 40

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 41

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

Incl 2 specific examples

Answer 41

Contralateral sensory changes and Impaired sensory recognition:

1) Asterognosis (steroanesthesia): inability to identify common objects on manual examination
2) Two point touch discrimination damaged which is more marked in the hands