Approach to Muscle Disorders (myositis)

Question 1

what is the difference between myositis an neuromuscular junction disorders?

Answer 1

both: weakness, fatigue, and atrophy

myopathy: myotonia, myalgia, cramps, contractures, ruppling/mounding, and muscle hypertrophy

neuromuscular junctions: exercise intolerance/fatiguability, muscle atrophy

Question 2

what questions to ask to assess proximal muscle weakness?

Answer 2

difficulty climbing stairs or standing from sitting
difficulty reaching above head or washing hair

Question 3

what are metabolic myopathies?

Answer 3

disorders of metabolism that result in muscle disorders dt the high energy requirements of muscles ➔ esp during exercise

also dt the build up of toxic metabolites within muscle cells

Question 4

how do metabolic myopathies usually present in children vs adults?

Answer 4

children: multisystemic disease ➔ failure to thrive dt the metabolic disorders

adult onset: isolated myopathies w/ exertional cramps

Question 5

examples of metabolic disorders that could cause myopathies

Answer 5

glycogen storage disorders
fatty acid oxidation defect disorders
organic acid disorders
mitochondrial disorders

Question 6

what are muscular dystrophies?

Answer 6

inherited diseases characterized by progressive weakness and degeneration of skeletal muscles +/- breakdown of nerve tissue

Question 7

what are 3 common muscular dystrophies?

Answer 7

Duchenne MD: MC childhood (toddler) ➔ absence of dystrophin ➔ progressive weakness and muscle wasting
- pseudohypertrophy of calves
- Gower’s sign: uses arms to sit up/stand up, almost as though their legs don’t work

Becker MD: ~11Y, muscle weakness in upper arms/shoulder ➔ upper legs nad pelvis ➔ toe walking, difficulty rising from floor

Myotonic dystrophy: 20-30Y, myotonia (unable to relax muscles post contraction) ➔ presents first in face/front of neck

Question 8

under muscular dystrophies there are also “congenital dystrophies” like ______

Answer 8

spinal muscular atrophy

Question 9

how do congenital dystrophies usually present?

Answer 9

from birth - <2Y
- usually a “floppy” baby ➔ diminished muscle tone - hypotonia
- progressive muscle weakness and degeneration - atrophy
- abnormally fixed joints - deformities and contractures
- spinal regidity
- motor milestone delays

Question 10

myopathies are characterized by prominent __________ proximal muscle weakness and ________ sensory changes

Answer 10

symmetric
absent

Question 11

def inflammatory myositis

Answer 11

chronic muscle inflammation, muscle weakness +/- muscle pain
- autoimmune disorder that attacks muscle fibers, blood vessels, connective tissue, organs, or joints

Question 12

def drug induced myopathies

Answer 12

drugs that cause muscle contraction/pain
ex. statins

Question 13

list the types of myositis (4)

Answer 13

polymyositis, dermatomyositis, immune-mediated necrotizing myopathy (rare), and inclusion body myositis (rare)

Question 14

def polymyositis

Answer 14

autoimmune progressive bilateral proximal muscle weakness in the hips, thighs, shoulders, upper arms, and neck

Question 15

def dermatomyositis

Answer 15

autoimmune progressive bilateral proximal muscle weakness (hips, shoulders, upper arms) with skin changes

Question 16

what specific clinical findings are present in dermatomyositis?

Answer 16

• heliotrope rash (around the eyelids/periorbital)
• shawl sign: rash on shoulders, chest, and back
• Gottron’s sign: extensor surface rash
• Gotton’s papules: papules on hand
• mechanic’s hands: dilated nail bed loops, thickened and cracked skin
• Holster sign: poikiloderma (rash w/ hypo, hyperpigmentation, telangiectasia and atrophy) on the lateral aspects of the thigh
• photosensitivity
• calcinosis cutis: calcium deposits under the skin/in muscle tissue

Question 17

what late stage complications can occur in myositis?

Answer 17

difficulty breathing, swallowing, arrhythmia, CHF

Question 18

how to ix a suspected myositis?

Answer 18

refer to rheum/neuro
- muscle enzymes: CK, AST, ALT, LDH, and aldolase
- urine: myoglobinuria ➔ r/o rhabdomyolysis
- consider autoimmune/rheum workup: ANA, anti-Jo1, anti-Mi2, anti-dsDNA/anti-smith
- Basic labs: CBC, Cr, lytes/ext lytes, liver function
- ESR/CRP ➔ inflammation
- consider malignancy work-up
- CXR and pulmonary function tests
- consider imaging: CXR, MRI

other:
- EMG and nerve conduction studies
- muscle biopsy ➔ not done often
- genetic testing

Question 19

how to tx myositis?

Answer 19

first line: corticosteroids
- can consider MXT if steroids AEs/need a LT couse or to help taper or if steroids have an inadequate response
- osteoporosis risk – bisphosphonates
- PPIs for LT steroid use or potential LT NSAID use

other:
- skin s/s: calcineurin inhibitors
- severe cases: IVIG or biologics like rituximab or plasmapheresis
- NSAIDs as needed
- pt education on LT corticosteroids: osteoporosis, steroid-induced myopathy, HTN, hyperglycemia, et gain
- physical exericse rehab
- avoid sunlight ➔ sunscreen
- aspiration precautions w/ oropharyngeal myopathy

Question 20

what are some ped red flags for a pediatric muscle disorder?

Answer 20

• increase CK > 3x normal
• fasciculations ➔ tongue
• dysmorphic features, organomegaly, signs of HF, and early joint contractures
• abnormalities on brain MRI
• resp insufficiency w/ generalized weakness
• loss of motor milestones ➔ not walking by 18M, regression of milestones
• motor delays present during minor acute illness