Peripheral Nerve & Skeletal Muscle Part 2 Flashcards
(34 cards)
What are some characteristics of traumatic neuromas?
Injury to nerve that regenerates slowly; axons continue to grow despite misalignment
- Small bundles of axons randomly oriented but surrounded by organized layers of Schwann cells, fibroblasts, and perineural cells
What are some kinds of compression or entrapment neuropathy?
- Carpal tunnel syndrome: Median nerve; paresthesia of tip of thump and first 2 digits
- Saturday night palse: Radial nerve when you fall asleep w upper arm raised
- Ulnar nerve at elbow, peroneal nerve at knee
- Morton neuroma
What is a main type of hereditary motor & sensory neuropathy?
Charcot-Marie-Tooth disease: Distal muscle atrophy, sensory loss, foot deformities
- Muscle pain
- Hand tremors
- Cold hands & feet
- Drop foot
- Curled toes
- High foot arches
- Breathing difficulties
What are some characteristics of NMJ diseases in general?
Impairment of ACh release leading to painless weakness & fatigue
- Autoantibodies that inhibit key NMJ proteins are the most common cause
What is Myasthenia Gravis?
What associations do we see?
Immune mediated loss of ACh receptors
- Often have autoantibodies to AChR
Strong association b/w AChR autoAbs and thymic abnormalities (often thymus hyperplasia)
What are some sx of Myasthenia Gravis?
Fluctuating generalized weakness that worsens w exertion & over the course of the day
- Weakness begins w extraocular muscles, drooping eyelids, double vision
Note: Those w muscle specific tyrosine kinase exhibit more focal muscle involvement
What is tx for Myasthenia Gravis?
- ACh-ase inhibitors (inc half-life of ACh)
- Plasmapheresis & immunosuppressives
- If thymoma, can get thymectomy
What is Lambert-Eaton Myasthenic Syndrome?
What are some sx and what is tx?
Antibodies block ACh release by inhibiting presynaptic calcium channel
- Paraneoplastic process often d/t small cell carcinoma of the lung
- Repetitive stimulation inc muscle response which is opposite of myasthenia gravis)
Tx: Drugs that inc ACh release
What are some characteristics of congenital myasthenic syndromes?
Present in the perinatal period w poor muscle tone, external eye weakness, breathing difficulties
- Others w milder form of disease may not come to clinical attention until adolescence or adulthood
D/Os caused by toxins
- What does Botox do?
- What is curare?
- Botox- Clostridium botulinum blocks release of ACh
- Curare causes flaccid paralysis (muscle relaxant during certain surgeries)
What are 3 distinct morphologic changes seen in myopathic injuries
Segmental myofiber degeneration & regeneration
- Creatinine kinase is released into blood (CK-MM)
- Regenerating fibers are rich in RNA (basophilic staining)
Myofiber hypertrophy
Cytoplasmic inclusions
What are 3 inflammatory myopathies?
- Dermatomyositis
- Polymyositis
- Inclusion body myositis
What is dermatomyositis?
What sx do we see? What antibodies do we see?
What pathologically causes this?
- Damage to small blood vessels
- Distinctive skin rash: Heliotrope discoloration of upper eyelids a/w periorbital edema
- Telangiectasias in nail folds, eyelids, gums
- Weakness and myalgias in proximal muscles
- Dysphagia
- Interstitial lung disease
- Cardiac involvement
Autoantibodies: Anti-Mi2, anti-Jo1, anti-P155/P140
What does dermatomyositis inc the risk of?
What is the histo?
What do we see in the juvenile form?
Inc risk of visceral cancer; may be viewed as paraneoplastic
Histo: “Perifascicular atrophy”
Juvenile: Calcinosis & lipodystrophy
What do we see clinically and histologically in immune-mediated necrotizing myopathy?
What can inc the risk for it?
Sx: Subacute muscle weakness a/w significantly inc creatine kinase levels
Muscle bx will show necrosis & regeneration while inflammatory cell infiltrates are usually absent or minimal despite the autoimmune nature of the disease
Prior stain exposure can inc risk
What do we see in polymyositis?
What cell type is involved?
Adult onset, myalgia and weakness, no cutaneous features (ddx from dermatomyositis)
- Symmetrical proximal muscle involvement
CD8+ cytotoxic T-cells in the endomysium
What is inclusion body myositis? Is it symmetric or asymmetric?
What do we see on histo?
Slowly progressive muscle weakness most severe in quadriceps & distal UE
- Starts w distal muscles esp extensors of knees and flexors of wrist and fingers
- Asymmetric
- Dysphagia
Rimmed vacuoles seen on histo
Tx for all inflammatory myopathies (dermatomyositis, polymyositis, inclusion body myositis)
Corticosteriods is first line
If steroid resistant, use immunosuppressives
Third line: IVIG. others
Note: Inclusion body myositis usually responds poorly to steroids or immunosuppressive tx
What can toxic myopathies be caused by? (5)
- Statins
- Chloroquine and hydroxychloroquine
- ICU myopathy esp cortocosteroids
- Thyrotoxic myopathies
- Alcohol
Dysfxnal gene in malignant hyperthermia?
Ryanodine receptor-1 gene
- RYR1
19q13.2
What are 2 X-linked muscular dystrophies? What gene are they caused by?
Both caused by lack of dystrophin, Xp21
Duchenne
- More severe phenotype (NO dystrophin
- Sx before 5yo, death between 25-30yo
- Dystrophin expressed in heart and CNS
Becker
- Nearly normal lifespan but have cardiac disease (dec amount of dystrophin)
What is pseudohypertrophy in DMD and what is muscle replaced by?
Enlargement of muscles of lower leg a/w weakness, inc bulk d/t inc muscle fibers initially but later in disease this is replaces by fat and connective tissue
What is myotonic dystrophy?
Multisystem disorder; skeletal muscle weakness, cataracts, endocrinopathy, cardiomyopathy
- Myotonia: Sustained involuntary contraction of muscles, can be elicited by percussion on thenar eminence
- Stiffness and difficulty releasing grip
Gait disturbances then atrophy of facial muscles leading to ptosis, “hatchet face”
What inheritance pattern is myotonic dystrophy passed on by? What do we see genetically?
What do we see on histo?
Autosomal dominant
CTG trinucleotide repeat
Myotonic dystrophy protein kinase (DMPK)
On histo can see “ring fiber”
