4.2: Defects in the sensory system Flashcards
Define the following terms A) hyperasthesia B) hyperalgesia C) Paraesthesia D) Dysaesthesia E) Allodynia
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
Describe the kind of pain that may be felt in a peripheral nerve lesion
Borders are sharply demarcated so identifying cause should be simple
Pain may involve hyperasthesia, discomfort or pain
Describe how pain may present in a nerve root lesion
How would pain NOT present in a nerve root lesion and why?
Sensory loss might be more vague but generally in dermatomal distribution. Pain may radiate
NOT anaesthesia due to overlap of dermatomes.
Describe how a spinal cord lesion may present
Mix of motor and sensory signs/symptoms
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?
1) Axonal degeneration – toxic, metabolic, physical
2) Demyelination
3) Vascular nerve damage (diabetes and peripheral vascular disease)
How might peripheral nerve damage present?
Give an example of a condition for each
1) Distal symmetrical neuropathy (diabetes)
2) Multifocal neuropathy (MS)
3) Mononeuropathy (MS)
What is a multifocal neuropathy and what is a mononeuropathy?
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)
What is multifocal neuropathy characterized by?
Progressive, asymmetrical muscle weakness and atrophy
Define the timelines for an acute, subacute and chronic peripheral nerve disease
Acute: <4 wks
Subchronic: 1-6 months
Chronic: >6 months
How might you investigate an individual with potential peripheral nerve damage?
Give an example of a condition when each is used
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)
What causes distal symmetrical neuropathy in diabetes and what vital mechanism of the body does this hinder?
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
List 2 things that should be recommended to a patient with diabetes
1) glycemic control
2) weight loss and expertise (especially type II)
What is the most common cause of neuropathy in the developed world?
What marker can we use to monitor this condition?
Diabetes
Marker: HBA1C
Why are amputations more commonly be performed in diabetics?
The vascular damage means the damage/infection has poor blood supply, and often cannot resolve despite antibiotics
What does GB syndrome predominantly affect and what is the classic presentation?
Motor nerves
Classically presents with ascending paralysis that ranges from mild weakness-complete paralysis
How many patients with GB syndrome require respiratory support? How is recovery and what is the mortality rate?
~20% require respiratory support
Recovery is spontaneous usually after a few weeks, mortality rate is 5%
How is GB syndrome managed and why?
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
Name four toxins which may cause a peripheral neuropathy
Lead, arsenic, mercury, ethanol
Name an infection which may cause a peripheral neuropathy
Leprosy
Name three nutritional deficiencies which may cause a peripheral neuropathy
Deficiencies in Thiamine, B12, niacin
Give some examples of foods containing niacin
What can a deficiency cause?
peas, broccoli, potatoes, mango avocado
Deficiency: 3Ds: diarrhea, dementia and dermatitis
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?
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.
Name four medications that can cause peripheral neuropathies and state what each is
Amiodarone (anti-arrhythmic), cis-platinum (chemo), isoniazid (antibiotic), and vincristine (chemo)
Name 4 systemic diseases that can cause peripheral neuropathies
1) Diabetes
2) cancer
3) sarcoidosis
4) uraemia
5) HIV/AIDS
What is carpel tunnel syndrome?
Compression of the median nerve at the wrist
Give 4 causes of carpal tunnel syndrome
1) Pregnancy
2) obesity
3) hypothyroidism
4) OA,
5) trauma
6) diabetes
7) acromegaly
Give 2 signs of carpel tunnel syndrome
1) Sensory changes
2) Muscles wasting and weakness
What 2 tests can be used to diagnose carpal tunnel syndrome?
Tinels: tap test
Phalen: stretch test
Nerve conduction studies can also be used to diagnose
Give 3 treatments for Carpal tunnel syndrome
1) splints, stretching (& weight loss)
2) steroid injections
3) surgical decompression
What is Meralgia paresthetica? (Hint: CK syndrome)
How would patient present?
Give 4 causes
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
What is the other name for Shingles and where does this virus lay dormant?
How does it present and the may this be extra concerning
How would we treat?
Herpes zoster: dormant in dorsal root ganglion
Shingles presents as a band of a painful rash that follows a dermatome. If it crosses a dermatome (bilateral) or is in multiple dermatomes (multidermatomal) they may be immunocompromised, so test for HIV etc)
Treat with Aciclovir (a topical capsaicin)
What is Brown-Sequard syndrome?
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
What happens below the lesion in brown-sequard syndrome and which spinal tracts are involved?
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
Give 4 potential causes of Brown-sequard syndrome
MS, trauma, tumour, disk degeneration
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?
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)
Give 4 conditions caused by B12 deficiency
1) Megaloblastic anaemia
2) Mental slowing
3) Dorsal columns affected
4) Cerebellar ataxia
5) Peripheral neuropathy
Where is Vit B12 metabolised and absorbed?
Metabolised in the stomach with intrinsic factor and absorbed in the ileum
What causes Pernicious anaemia and how would you treat?
Autoantibodies to parietal cells or intrinsic factor
Treatment: hydroxycobalamin
Describe the pathology of Syringomyelia, which ascending sensory tract is damaged?
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
Describe the sensation loss and pain that occurs in a Thalamic brain lesion
Name one disease where this occurs
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)
Describe the sensational changes that occurs in a sensory cortex brain lesion
Incl 2 specific examples
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
