PNS Pathology Flashcards
What are the three general classes of peripheral nerves? What information does each transmit?
- large myelinated: motor, proprioception, fine touch, vibration, 2-point discrimination
- small myelinated: pain and temperature
- small unmyelinated: also pain and temperature
What is the temporal evolution of most peripheral neuropathies?
- most are slow and insidious; chronic
- in cases with acute or subacute development (2 months or less): suspect GBS, vasculitis, infection (Lyme disease), etc.
How can we determine whether or not a neuropathy is targeting the myelin or the actual axon?
- use nerve conduction studies (NCS) and an electromyography (EMG)
- in demyelination: conduction velocity will decrease, latency period will increase, and there will be no fibrillations
- in axonal damage: amplitude of the potentials will decrease, and there will be fibrillations
What are the most common causes of small-fiber (loss of pain and temp) peripheral neuropathy?
- diabetes mellitus / glucose intolerance
- amyloidosis
- (diabetes is the most common cause of peripheral neuropathy in the developed world)
What is mononeuropathy multiplex? What are the most common causes?
- mononeuropathy multiplex is when two or more separate nerves are affected
- vasculitis, hepatitis, Lyme disease, HIV
What are the two conditions where nerve biopsy is indicated?
- in amyloid neuropathy and in vasculitis
- otherwise, it is rarely indicated
Compare radiculopathy, plexopathy, mononeuropathy, and polyneuropathy. What are the most common causes of each?
- radiculopathy: spinal root is affected (herniated disk, Lyme disease)
- plexopathy: brachial or lumbosacral plexus is affected (trauma, tumor invasion, compression, viral infection)
- mononeuropathy: solitary peripheral nerve affected (trauma, compression, entrapment)
- polyneuropathy: multiple nerves simultaneously affected; usually is length-dependent (glove and stocking), affecting lower limbs before upper limbs (GBS, diabetes)
What are common causes of acute polyneuropathy? Chronic polyneuropathy?
- acute: Guillian-Barre syndrome
- chronic: inflammatory (CIDP, vasculitis), infection (leprosy, HCV, HIV), inherited (Charcot-Marie Tooth), metabolic (diabetes, thyroid disease, liver failure), toxic (alcohol), nutrition (vit B12 deficiency), systemic (RA, sarcoidosis, Sjogren’s syndrome), malignancy
What are the most prevalent causes of chronic polyneuropathy?
- diabetes, HIV, uremia, and alcohol
How common are changes in mental status in peripheral neuropathy?
- changes in mental status are rare in peripheral neuropathy (exceptions are with alcohol, uremia, or in the setting of hyperosmolar hypoglycemia in diabetics)
What is peripheral neuropathy? How do patients commonly present?
- any disorder that affects the nerve structures beyond the spinal cord
- most common presentation: sensory change (loss if destructive, paresthesias if irritative)
- motor symptoms (gait and balance instability) are less common; muscle weakness is a late sign
- (this is because smaller fibers, which deal with sensation, are usually more affected than larger fibers, which control movement)
What is Charcot-Marie-Tooth disease? What deformity is commonly associated with this disease? What gene is mutated?
- a group of inherited disorders affecting the peripheral nervous system (most are A.D.)
- look for muscle wasting and sensory loss
- many patients have pes cavus (a high-arched foot with flexion of the small toes, called “hammer toes”)
- results from mutations in the PMP22 gene (this codes a protein in the myelin sheath)
Diabetes is associated with several different patterns of neuropathy - what are they? Which is the most common?
- most common pattern: distal and symmetrical, with sensory-greater-than-motor neuropathy (AKA distal symmetrical sensorimotor polyneuropathy)
- others: painful, asymmetric, proximal-to-distal pattern (AKA lumbosacral radiculopathy); mononeuropathy multiplex pattern; pure autonomic neuropathy pattern (AKA autonomic neuropathy)
What primary investigations should we order for patients presenting with signs of peripheral neuropathy?
- nerve conduction studies (NCS) and electromyography (EMG)
- CBC, electrolytes
- fasting blood glucose, HbA1c (diabetes)
- ESR, CRP (inflammation)
- TSH, B12, folate (metabolic, nutritional)
- rheumatoid factor, auto-antibodies
- LFTs, urinalysis (liver and kidney failure)
What is Guillian-Barre Syndrome? How do patients classically present? How do we treat it?
- a relatively common life-threatening disease of the PNS; autoimmune destruction of Schwann cells
- rapidly progressing acute demyelinating disorder of motor neurons; due to an autoimmune response (usually following an infection) via molecular mimicry (antibodies target ganglioside cells)
- classic presentation: ascending weakness and paralysis (motor deficits are greater than sensory deficits)
- patients can die from respiratory failure once these muscles are affected (30% will require ventilation)
- treat with plasmapheresis and IVIG (however, in patients that are IgA deficient or who have renal failure, only give plasmapheresis)
What percentage of patients with Guillian-Barre Syndrome report a preceding respiratory or GI infection? What are the most common causes of GBS?
- 50-70% of patients report a previous recent infection (GIT or respiratory)
- Campylobacter jejuni is major cause
- others: Epstein-Barr Virus, cytomegalovirus, and HIV
What is CIDP?
- chronic inflammatory demyelinating polyneuropathy
- similar to GBS, but with a chronic, relapsing-remitting course
- also unlike GBS, this affects both motor and sensory nerves (GBS is mainly motor)
- treat with plasmapheresis and immunosuppression
Lumbosacral pain (lower back pain) must be between which vertebral segments?
- lower back pain: between T12 and S1
- above T12: thoracic pain
- below S1: buttock pain
Which portions of the intervertebral disc contain pain fibers?
- only the outer 1/3 of the anulus fibrosis (so the outermost area) contains pain fibers
What type of pain is most common in lumbosacral pain? (mechanical/somatic, disc, spinal, visceral referred pain)
- mechanical/somatic pain contributes to 85-90% of lumbosacral pain cases
- pain here rarely radiates past the knee
- (often, however, no specific cause can be found - making this a functional problem, not a structural one)
What is sciatica?
- Sciatica is irritation of the sciatic nerve, resulting in radicular pain (the leg pain is usually worse than the back pain and often radiates past the knee)
What usually causes cauda equina syndrome? What can result from this syndrome? What are the most common findings in patients with cauda equina syndrome?
- usually caused by a large central disc protrusion
- cauda equina syndrome can result in unilateral or bilateral sciatica
- most common findings are urinary incontinence and saddle area anesthesia (and impotence)
What vertebral segments does the straight leg raise test for radiculopathy? What about the femoral stretch test?
- straight leg raise: L5 and S1
- femoral stretch: L2, L3, and L4
What are the major principles in managing a patient with lower back pain? What percentage of people will regain function with decreasing pain?
- AVOID routine imaging and AVOID bed rest
- give simple analgesics (paracetemol), and encourage as much physical activity as possible
- if no improvement, give stronger pain killers (NSAIDs or stronger opiate), and suggest physical therapy
- screen for red and yellow flags
- 90% of patients will recover function and have decreasing pain after 6-12 weeks
Why is routine imaging often contraindicated in patients with lower back pain?
- because 94% of these patients end up having NSLBP (non-specific lower back pain) with no apparent cause (and therefore no real cure)
- save imaging for the 1% with serious pathology (cancer, infection, fracture, cauda equina syndrome, ankylosing spondylitis)
Of the patients with lower back pain, 94% have NSLBP (non-specific lower back pain), 5% have radiculopathy, and 1% have serious pathologies - how do we determine who gets imaging?
- (imaging should only be used for the 1% with serious pathology)
- look for red flags indicating a more serious pathology!
- cancer: weight loss, night pain, young or old age
- infection: fever, IV drug use, immunocompromised
- fracture: osteoporosis, trauma, old age, extended corticosteroids
- ankylosing spondylitis: younger age
- cauda equina: incontinence, impotence, saddle anesthesia
Which vertebral discs have the greatest risk of herniation?
- the lumbar disks because these bear the most pressure
What’s the most common area and cause of lumbosacral radiculopathy?
- 90% are in the L4-L5 or L5-S1 region, and are secondary to lumbar disc herniation
- assess with straight leg raise
Which investigations can help in the diagnosis of GBS?
- lumbar puncture!
- this is a disease of the PNS, but parts of the spinal roots lie in the subarachnoid space, so inflammation here results in protein leaking out into the SAS/CSF
- however, they will not be leaky enough for WBCs to enter, and so the CSF cell count is normal
- this is called albumino-cytological dissociation
- also: NCS (decreased velocity b/c demyelination)
