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 well demarcated and may involve hyperasthesia, discomfort or pain
Describe how pain may present in a nerve root lesion
Sensory loss might be more vague but generally in dermatomal distribution, not anesthesia due to overlap of dermatomes. Pain may radiate
Describe how a spinal cord lesion may present
Mix of motor and sensory signs/symptoms
Name two examples of vascular nerve damage
Diabetes and peripheral vascular disease
How might peripheral nerve damage present?
- Distal symmetrical neuropathy
- Multifocal neuropathy
- Mononeuropathy
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?
- Nerve conduction studies; stimulates specific nerves and records their ability to send impulses to the muscle
- CSF
- Biochemistry; toxins
Names one example of a toxin which may accumulate and cause neuropathies
Renal failure may cause a buildup of urea
What causes distal symmetrical neuropathy in diabetes and what vital mechanism of the body does this hinder?
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
How many diabetes will experience neurophysiological signs after 10 years?
Nearly 100%
What is the most common cause of neuropathy in the developed world?
Diabetes
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?
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
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 factors which may cause a peripheral neuropathy
Deficiencies in thiamine, B12, niacin
Where would niacin be found and what can it cause?
Certain legumes, may cause the 3 Ds: diarrhea, dementia and dermatitis
How does a B12 deficiency affect the nervous system? How is a B12 deficiency (And pernicious anemia) treated?
Damages the myelin sheath that surrounds and protects nerves, can give hydroxycobalamin
Name five systemic diseases that can cause peripheral neuropathies
Diabetes, cancer, sarcoidosis, uraemia, HIV/AIDS
Name four medications that can cause peripheral neuropathies
Amiodarone (anti-arrhythmic), cis-platinum (chemo), isoniazid (antibiotic), and vincristine (chemo)
What causes brown-sequard syndrome and how does it present?
Hemisection of spinal cord (incomplete spinal injury) with hemiparaplegia on one side and hemianaesthesia on the other side
What happens below the lesion in brown-sequard syndrome and which spinal tracts are involved?
- Ipsilateral Upper motor neurone weakness - corticospinal tracts are affected which may leads to spastic paralysis, brisk reflexes and upgoing plantars
- Ipsilateral loss of proprioception and vibration - dorsal columns
- Contralateral loss of pain and temperature - lateral spinothalamic tract
Name four potential causes for brown-sequard syndrome
MS, trauma, tumour, disk degeneration
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?
B12 deficiency, slow onset. Causes symmetrical dorsal column loss but even in severe cases the spinothalamic tracts are preserved (don’t know why)
Where is B12 stored in the body and how long does storage last before depletion occurs?
Liver, 4 years
Where is B12 metabolized and absorbed in the body?
Metabolized (along with intrinsic factor from stomach lining cells) in the stomach and absorbed (carried by intrinsic factor) in the ileum
Name five conditions associated with B12 deficiency (not including pernicious anemia)
“My diet can make problems”
- Megaloblastic anemia: insufficient amount and abnormally large RBCs
- Mental slowing
- Dorsal columns affected
- Cerebellar ataxia
- Peripheral neuropathy
Other than a B12 deficiency, what can cause pernicious anemia?
Autoantibodies against intrinsic factor or parietal cells
Describe the pathology of syringomyelia, which ascending sensory tract is damaged?
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.
Which regions of the spinal cord and which regions of the body are commonly affected by syringomyelia?
Spine: Commonly the lower cervical/upper thoracic
Body: upper limbs (‘cape-like’ distribution)
What are four potential causes for syringomyelia?
Congenital, trauma, idiopathic, tumour
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
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
Name the two pathologies which give rise to “glove and stocking” sensory loss
Demyelination and axonal degeneration
What rare lesion affects the dorsal roots and columns and is a late symptom of syphilis?
Tabes dorsalis
What is sensory ataxia?
Movement disorder arising from the loss of sensory input necessary for motor feedback
What is a positive Romberg sign and with what lesions would it be seen?
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
What is sensory agnosia?
Loss of ability to recognize objects, faces, places or voices
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?
- Prolonged B12 deficiency causes degenerative changes in the dorsal columns
- This leads to sensory agnosia, which in turn reduces pressure and touch sensations from the limbs - causing a loss of position sense
- 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
Why is sensory loss bilateral in syringomyelia?
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
What symptoms (including sensory) are you likely to experience in syringomyelia?
Bilateral sensory loss: loss of sensation in hands, temperature loss
Disturbances in the ANS
