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USMLE Step 1 > Muskuloskeletal System > Flashcards

Muskuloskeletal System Flashcards

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1
Q

Name the carpal bones

A

Some = scaphoid (most common break)

Lovers = Lunate (most common dislocation)

Try = triquentum

Positions = pisiform

That = trapezium (by the thumb)

They = trapezoid (looks like a trapezoid)

Can’t = capitate

Handle = hamate

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2
Q

Denosumab

A

Monoclonal antibody against RANKL

Indicated for treatment of osteoporosis

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3
Q

Osteopetrosis

A

Carbonic anhydrase II defect leads to decreased acidification and failure of osteoclasts

Abnormally thick, stone-like but brittle bone, long ends of the bone are thicker than the middle (Erlenmeyer flask deformity)

Bone fills marrow space → pancytopenia, extramedullary hematopoiesis

Narrowing foramina → cranial nerve impingement and palsies

Tx: bone marrow transplant

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4
Q

Rickets/Osteomalacia

A

Vitamin D deficiency → defective mineralization/calcification of osteoid

Rickets in children - bowed legs, pigeon-break deformity, enlarged forehead, rachitic rosary

Osteomalacia in adults - soft bones

Labs: ↓ calcium, ↓ phosphate, ↑ PTH, ↑ ALP

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5
Q

Paget disease of bone

A

Imbalance between osteoclast and osteoblast activity

Increased bone but disordered and weak → fractures easily

Mosaic pattern of woven and lamellar bone (see picture)

Increasing hat size, nerve compression → hearing loss

↑ risk of osteosarcoma

Labs normal except ↑ ALP

Tx: calcitonin, bisphosphonates

Stages:

  1. Osteolytic via osteoclasts
  2. Mixed
  3. Osteosclerotic via osteoblasts
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6
Q

Osteogenesis Imperfecta

A

Autosomal dominant defect in synthesis of collagen type 1 by osteoblasts, fibroblasts → impairmement of bone matrix formation

Type II is fatal in utero

Type I - increased fractures in childhood, blue sclera (thinning of scleral collagen exposes choroidal veins), hearing loss, dental abnormalities, often mistaken for child abuse

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7
Q

Giant cell tumor

A

Benign tumor in the epiphyseal end of long bones, especially the knee

20-40 y/o

Multinucleated giant cells in a background of stromal cells

“Soap bubble” appearance on x-ray

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8
Q

Osteochondroma

A

Most common benign tumor of bone

Males < 25 y/o

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9
Q

Osteosarcoma

A

Malignant mesenchymal tumor of osteoblasts often found in the metaphysis of long bones (femur, tibia)

Bimodal distriution: 10-20, > 60 y/o

Risk factors include: Paget disease of the bone, bone infarcts, familial retinoblastoma, Paget disease, radiation exposure, Li-Fraumani (germline p53 mutation)

Codman triangle (elevation of periosteum) or sunburst pattern on x-ray

20% have pulmonary metastases at time of diagnosis

Tx: resection + chemotherapy

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10
Q

Ewing sarcoma

A

Malignant tumor of poorly-differentiated cells derived from neuroectoderm commonly in diaphysis of long bones, pelvis scapula, ribs

Associated with t(11;22)

Boys < 15 y/o

Onion-skin layering, IMC stain for CD99

Tx: neoadjuvant chemo, surgery, radiation

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11
Q

Chondrosarcoma

A

Malignant cartilaginous tumor

Expansile glistening mass within the medullary cavity

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12
Q

X-ray findings for osteoarthritis vs. rheumatoid arthritis

A

Osteoarthritis: subchondral cysts, sclerosis, osteophytes, eburnation, joint space narrowing

Rheumatoid arthritis: pannus formation, one and cartilage erosions, increased synovial fluid

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13
Q

Clinical features of osteoarthritis vs. rheumatoid arthritis

A

Osteoarthritis: DIP involvement, Heberden nodes (DIP), Bouchard nodes (PIP), no MCP involvement, pain increases with use

Rheumatoid arthritis: DIP sparing, subcutaneous rheumatoid nodules (fibrinoid necrosis), ulnar deviation of fingers, Baker cyst, morning stiffness that improves with use

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14
Q

Sjogren Syndrome

A

Autoimmune destruction of exocrine glands (especially lacrimal and salivary)

Characterized by xeropthalmia, xerostomia, bilateral parotid enlargement → dental caries, MALT lymphoma

Anti-SS-A/Ro and anti-SS-B/La

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15
Q

Gout vs. pseudogout crystals

A

Gout = monosodium urate crystals are negatively birefringent, needle-shaped, yellow in parallel light and blue in perpendicular light

Acute tx: NSAIDs, glucocorticoids, colchicine

Chronic tx: allopurinol, febuxostat (xanthine oxidase inhibitors)

Pseudogout = calcium pyrophosphate crystals are weakly positively birefringent, rhomoid-shaped, and blue in parallel light

Tx: NSAIDs, glucocorticoids, colchicine

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16
Q

Polymyositis

A

Autoimmune endomysial inflammation with CD8+ T cells (overexpression of MHC class I on the sarcolemma)

Characterized by progressive symmetric proximal muscle weakness, often involving the shoulders

Labs: ↑ CK, +ANA, + anti-Jo-1 (histidyl-tRNA synthase), + anti-SRP, + anti-Mi-2

Complications: interstitial lung disease, myocarditis

Tx: steroids

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17
Q

Dermatomyositis

A

Autoimmune perimysial inflammation with CD4+ T cells

Characterized by progressive symmetric proximal muscle weakness, malar rash, Gottron papules, heliotrope rash, “shawl and face” rash, “mechanic’s hands”

↑ risk of occult malignancy

Labs: ↑ CK, +ANA, + anti-Jo-1, + anti-SRP, + anti-Mi-2

Tx: steroids

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18
Q

Myasthenia gravis

A

Autoantibodies to postsynaptic acetylcholine receptors

Characterized by ptosis, diplopia, weakeness that worsens with muscle use

Associated with thymoma, thymic hyperplasia

Tx: acetylcholinesterase inhibitors

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19
Q

Lambert-Eaton

A

Autoantibodies to presynaptic voltage-gated calcium channel → ↓ acetylcholine release

Characterized by proximal muscle weakness and improves with muscle use, autonomic symptoms (dry mouth, impotence), cranial nerve involvement (esp. oculobulbar)

Associated with small cell lung cancer

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20
Q

Systemic sclerosis

A

Excessive fibrosis and collagen deposition

Diffuse scleroderma: widespread skin involvement, rapid progression, early visceral invovlement (renal, pulmonary, cardiovascular, GI), anti-DNA topoisomerase I/Scl-70

Limited scleroderma/CREST: involvement limited to skin of fingers and face, calcinosis, Raynaud phenomenon, esophageal dysmotility, sclerodactyly, telangiectasia, anti-centromere

Cx: pulmonary arterial hypertension → cor pulmonale → right heart failure

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21
Q

Albinism

A

Failure of neural crest cell migration or normal melanocyte number with decreased melanin production due to decreased tyrosinase actiity of defective tyrosine transport

↑ risk of skin cancer

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22
Q

Psoriasis

A

Chronic inflammatory dermatosis causing excessive keratinocyte proliferation, possibly autoimmune

Sharply demarcated erythematous or salmon-colored papules and plaques covered by white, silvery scales, on the scalp, sacral region, extensor surfaces of the extremities, umbilicus, penis, nails

Epithelial hyperplasia (acanthosis), parakeratotic scaling (excess keratin and retention of nuclei in stratum corneum), elongation of rete ridges, elongation of papillary dermis and thinning of epidermis (pinpoint bleeding = Auspitz sign), collections of neutrophils in stratum corneum (Munro microabscesses)

Tx: vitamin D analogs (calcipotriene, calcitriol, tacalcitol), cyclosporine, etanercept, methotrexate, ustekinumab (anti-IL-12 and IL-23)

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23
Q

Seborrheic keratosis

A

Benign squamous cell proliferation

Flat, round, pigmented (pale to dark brown), sharply demarcated lesions, “stuck-on” appearance, warty, waxy, or greasy surface on the trunk, face, neck, extremities

Hyperkeratosis, acanthosis, papillomatosis, melanocytic hyperplasia, horn cysts, keratin pseudocysts

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24
Q

Leser-Trelat sign

A

Leser-Trelat sign is the sudden onset of multiple seborrheic keratoses and suggests underlying carcinoma of the GI tract

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25
Q

Pemphigus vulgaris

A

IgG autoantibodies directed against desmoglein (1, 3) in desmosomes causing epidermal cell detachment → reticular/net-like pattern on immunofluorescence

Painful mucosal mouth ulcers, blisters/bullae on the face, scale, torso, Nikolsky +

A/w drugs, SLE, HIV, HSV

Poor prognosis

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26
Q

Bullous pemphigoid

A

IgG autoantibodies directed against hemidesmosomes between basal cells and basement membrane → linear immunofluorescence

Severe pruritus, tense blisters/bulla on the trunk and extremities that do not rupture easily, Nikolsky -

More commonly seen in the elderly (> 70) and a/w drugs and neurologic disorders

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27
Q

Dermatitis herpetiformis

A

IgA antibodies formed against gliadin protein in gluten cross-reacts with reticulin that is a component of the anchoring fibrils that attach the basement membrane to the dermis → IgA localization at tips of dermal papillae

Pruritic vesicles and bullae that are grouped (herpetiform)

Strong association with celiac disease

Tx: gluten-free diet

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28
Q

Staphylococcal scalded skin syndrome

A

Staph produces an exotoxin that destroys keratinocyte attachents in the stratum granulosum only

Characterized by fever, generalized erythematous rash with sloughing of the upper layers of the epidermis that heals completely

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29
Q

Stevens-Johnson syndrome

A

Often associated with adverse drug reaction

Characterized by fever, bulla formation and necrosis, sloughing of skin, erythema multiforme-like target lesions, typically involves 2 mucous membranes, Nikolsky +, and a high mortality rate

Toxic epidermal necrolysis is a more severe form that involves > 30% of the body surface area

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30
Q

Acanthosis nigricans

A

Epidermal hyperplasia (↑ spinosum) causing symmetrical, hyperpigmented, velvety thickening of skin, espeially on the neck and axilla

A/w hyperinsulinemia (diabetes, obesity, Cushing syndrome) and visceral malignancy

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31
Q

Erythema multiforme

A

Hypersensitivity reaction to infection (HSV, mycoplasma), drugs (penicillin, sulfonamides), or autoimmune (SLE) mediated by cytotoxic T lymphocytes or CD4 cells

Macules and papules with a red or vesicular center; acral, bilateral, symmetric, targetoid due to central necrosis surrounded by erythema

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32
Q

Actinic keratosis

A

Premalignant lesions caused by sun exposure

Small, rough/sandpapery, scaly, erythematous or brownish papules or plaques on sun damaged skin (face, arms, back, dorsal hands)

Risk of squamous cell carcinoma proportional to degree of epithalial dysplasia

33
Q

Erythema nodosum

A

Inflammatory reaction that affects connective tissue between fat lobules

Painful erythematous plaques, usually on anterior shins

Can be idiopathic or associated with sarcoidosis, coccidioidomycosis, histoplasmosis, TB, strep, leprosy, and Chron’s disease

34
Q

Lichen planus

A

6 Ps: pruritic, purple, polygonal, planar (flat) papules and plaques

Mucosal involment (reticular white lines) = Wickham striae

Saw-tooth infiltrate of lymphocytes at dermal-epidermal junction

Associated with chronic hepatitis C infection

35
Q

Basal cell carcinoma (most common skin cancer)

A

Malignant proliferation of basal cells in the epidermis

Risk factors: sun exposure (UVB-induced damage; pyrimidine dimers), albinism, xeroderma pigmentosum (autosomal recessive defect in nucleotide excision repair)

Gross: nodular, slowly enlarging, pink, pearly papule, may have telangiectasia and central ulceration, rolled borders often found on the head, neck, trunk, upper lip

Histology: nodules/islands of basal cells with peripheral palisading

Prognosis: locally invasive but rarely metastasizes

Tx: surgical excision

36
Q

Squamous cell carcinoma

(second most common skin cancer)

A

Malignant proliferation of squamous cells in the epidermis

Risk factors: sun exposure (UVB-induced damage; pyrimidine dimers), albinism, xeroderma pigmentosum (autosomal recessive defect in nucleotide excision repair), scarring from burn injury, irradiation, arsenic poisoning, immunosuppression

Gross: nodule with central ulceration and pink, elevated, indurated border that does not heal spontaneously on the face, lower lip, ears, hands

Histology: keratin pearls

Prognosis: locally invasive, may spread to local lymph nodes, but rarely metastasizes

Tx: surgical excision

37
Q

Melanoma

A

Malignant neoplasm of melanocytes; associated with mutation in BRAF protein kinase

Risk factors: sun exposure (UVB-induced damage; pyrimidine dimers), albinism, xeroderma pigmentosum (autosomal recessive defect in nucleotide excision repair), dysplastic nevus syndrome

Variants: superficial spreading, nodular (early vertical growth), lentigo maligna, acrolentiginous (palms and soles, not a/w UV)

Look for: asymmetry, borders irregular, color variations, diameter > 6 mm, evolution over time

Prognosis: radial (good prognosis) vs. vertical growth (bad prognosis – Breslow tumor depth measured between top of granular layer and the deepest point of invasion)

Tx: surgical excision with wide margins

38
Q

Bisphosphonates

A

Pyrophosphate analog that binds to hydroxyapatite in bone and inhibits osteoclast activity via increased apoptosis and reduced development/recruitment

Indicated for osteoporosis, hypercalcemia, Paget disease of bone

SA: corrosive esophagitis, osteonecrosis of the jaw, atypical femur fractures with prolonged use

39
Q

Colchicine

A

Binds and stabilizes tubulin to inhibit microtubule polymerization, impairing leukocyte chemotaxis and degranulation

Indicated for acute treatment of gout (NSAIDs are first line)

SA: diarrhea, nausea, vomiting, abdominal pain

40
Q

Allopurinol

A

Inhibits xanthine oxidase to decrease convertion of xanthine to uric acid

Indicated for chronic treatment of gout and to prevent tumor lysis-associated urate nephropathy

41
Q

Febuxostat

A

Inhibits xanthine oxidase to decrease convertion of xanthine to uric acid

Indicated for chronic treatment of gout and to prevent tumor lysis-associated urate nephropathy

42
Q

What drugs should you avoid in patients with gout?

A

Salicylates (low-dose) and thiazide diuretics

Both decrease renal tubular excretion of uric acid

43
Q

Probenecid

A

Inhibits reabsorption of uric acid in the proximal convoluted tubule

44
Q

Etancercept

A

Fusion protein (receptor for TNF-α + IgG1 Fc)

Indicated for rheumatoid arthritis, psoriasis, ankylosing spondylitis

SA: infection (TNF blockade prevents activation of macrophages and destruction of phagocytosed microbes)

45
Q

Infliximab

A

Anti-TNF-α

Indicated for IBD, rheumatoid arthritis, psoriasis, ankylosing spondylitis

SA: infection (TNF blockade prevents activation of macrophages and destruction of phagocytosed microbes)

46
Q

Adalimumab

A

Anti-TNF-α

Indicated for IBD, rheumatoid arthritis, psoriasis, ankylosing spondylitis

SA: infection (TNF blockade prevents activation of macrophages and destruction of phagocytosed microbes)

47
Q

How is estrogen protective of bone mineral density

A

Estrogen stiimulates osteoclast apoptosis, suppresses osteoblast apoptosis, and reduces levels of pro-resorptive cytokines

48
Q

Describe the role of RANKL and OPG in bone regulation

A

RANKL and OPG is produced by osteoblasts

RANKL binds to RANK on osteoclasts and stimulates proliferation and differentiation

OPG has the opposite affect

49
Q

Xeroderma pigmentosum

A

Autosomal recessive defect in nucleotide excision repair (endonucleases that recognize thymine dimers and excise the short stretch of ssDNA around them)

Characterized by photosensitivity, poikiloderma, hyperpigmentation in sun-exposed areas, and skin cancer

50
Q

Describe the pathway of collagen synthesis

A

Collagen consists of 3 polypeptide α-chains in a triple helix held together by hydrogen bonds. The amino acid sequence is repetitive (Gly-X-Y)n with Gly being necessary in every third position to ensure compact coiling.

It is synthesized by fibroblasts, osteoblasts, and chondroblasts through the following steps:

  1. Translation begins in the cytoplasm and an signal at the N-terminus of the pre-pro-α-chain facilitates binding to the RER
  2. In the RER, the pre-pro-α-chain is cleaved to form pro-α-chain
  3. Proline and lysine at the Y positions are hydroxylated (vitamin C dependent)
  4. Some hydroxylysine residues are glycosylated
  5. Disulfide bonds between the C-terminals of 3 α-chains align the procollagen
  6. Procollagen is transported through the Golgi into the extracellular space
  7. The N- and C-terminal propeptides are cleaved by procollagen peptidases converting the molecule into a less soluble tropocollagen
  8. Tropocollagen monomers self-assemble into collagen fibrils
  9. Lysyl oxidase creates covalent crosslinks between collagen fibrils
51
Q

Ehlers-Danlos syndrome

A

Hereditary disorders characterized by defective collagen type IV synthesis (e.g. mutated procollagen peptidase)

Characterized by joint laxity, hyperextensible skin, fragile tissue with easy bruising, poor wound healing → soluble collagen that does not properly crosslink

52
Q

Vitiligo

A

Partial or complete loss of epidermal melanocytes

53
Q

Describe normal wound healing

A
  1. Days 0-1: vasoconstriction, platelet aggregation, fibrin deposition
  2. Days 1-3: neutrophil migration and macrophage phagocytosis of necrotic debris and bacterial contaminants
  3. 3 days - 3 weeks: fibroblasts form connective tissue + endothelial cells begin to form blood vessels → granulation tissue, wound contraction
  4. 3+ weeks: fibroblasts continue to synthesize connective tissue matrix (collagen, elastin), slow, progressive increase in tensile strength of new tissue

Excess TGF-β → excess and disorganized collagen production can cause a keloid/hypertrophic scar

Excess metalloproteinase activity and myofibroblast accumulation → contractures

54
Q

Acrochorda

A

Skin tag

55
Q

Ephelides vs. solar lentigines

A

Ephelides (freckles) = increased melanin production by melanocytes

Solar lentigines = increased proliferation of melanocytes, more common in adults

56
Q

Types of nevi

A

Melanocytic nevi are benign neoplasms of mitotically quiescent melanocytes

Junctional nevus: malenocytes limited to the dermoepidermal junction, flat, darker coloration in the center than the periphery

Compound nevus: melanocytes extend into the dermis, raised, uniformly pigmented

Intradermal nevus: nests of melanocytes are lost and remaining cell lose tyrosinase activity and produce little pigment, dome-shaped or pedunculated lesions

57
Q

Angiosarcoma

A

Malignant tumor of endothelial origin

Can be located in the liver or cutaneously (Stewart-Treves)

Increased risk with chronic lymphedema (e.g. post-radical mastectomy with axillary lymph node dissection)

Associated with exposure to arsenic, vinyl chloride

58
Q

Histology of atopic dermatitis (eczema) vs urticaria

A

Atopic dermatitis (eczema) → epidermal spongiosis (intercellular epidermal edema)

Urticaria → dermal edema

59
Q

Polyarteritis nodosa

A

Multisystem involvement with segmental, transmural inflammation of the arterial wall with fibrinoid necrosis seen in young adults

Renal: glomerulonephritis, HTN

Nervous: peripheral neuropathy

GI: mesenteric ischemia

MSK: myositis, arthritis

Associated with hepatitis B

60
Q

Endochondral vs. intramembranous ossification

A

Endochondral ossification = long bones are formed when mesenchymal cells differentiate into chondroblasts which secrete cartilage matrix → cartilage template → calcification and invasion by osteoblasts, osteoclasts, and blood vessels from the periosteum → woven bone undergoes remodeling into compact bone

Intramembranous ossification = skull bones are formed when mesenchymal cells differentiate directly into osteoblasts and begin osteoid matrix secretion without the formation of cartilagnious bone

61
Q

Pathology of long bones by location

A

Epiphysis: giant cell tumor

Metaphysis: hematogenous osteomyelitis in children (vertebra in adults), osteosarcoma

Diaphysis: Ewing sarcoma, chondrosarcoma

62
Q

McCune-Albright syndrome

A

Mosaic somatic mutation in the BNAS gene encoding stimulatory α subunit of G protein → constitutive activation of adenylate cyclase

Characterized by cafe-au-lait spots, endocrine abnormalities (e.g. precocious puberty, hyperthyroidism), and fibrous dysplasia (osteolytic-appearing lesions in bone)

63
Q

Legg-Calve-Perthes disease

A

Isolated idopathic osteonecrosis of the hip in young children

64
Q

Rotator cuff exam

A

Damage to supraspinatus (most common) → limited or painful abduction (esp. first 10-15 degrees then deltoid helps)

Damage to infraspinatus and/or teres minor → limited or painful external rotation

Damage to subscapularis → limited or painful internal rotation

65
Q

Duchenne muscular dystrophy

A

X-linked recessive deletion of the dystrophin gene, a structural protein of muscle fibers

Onset at age 2-5 with ambulation difficulties, Gower sign, calf pseudohypertrophy (fibrofatty muscle replacement), kyphoscoiosis

Complications: wheelchair bound by age 12, worsening scoliosis c/b restrictive pulmonary function

66
Q

Most common shoulder dislocation

A

Anterior dislocation (impact while arm in the overhead throwing position) → flattening of the deltoid leads to “square shoulder” deformity, axillary nerve may be injured

67
Q

Lateral vs. medial epicondylitis

A

Lateral epicondylitis AKA “tennis elbow” is caused by overuse of the wrist extensors

Medial epicondylitis AKA “golfers’ elbow” is caused by overuse of the wrist flexors

68
Q

MSK nerve injuries to the lower extremities

A

Damage to obturator nerve (traverses obturator canal) → weakness of thigh adductor muscles, sensation over distal medial thigh

Compression of the neck of the fibula (lateral) → compression of common peroneal (fibular) nerve:

Deep peroneal nerve (anterior compartment) → weakness of foot dorsiflexion (foot drop), impaired sensation of the webspace between the first and second toes

Superficial peroneal nerve (lateral compartment) → weakness of foot eversion and impaired sensation of the lateral shin and dorsal foot

Tibial nerve damage (posterior compartment) → weakness of foot plantarflexion, inversion, toe flexion (difficulty standing on toes) and impaired sensation over the sole

69
Q

Brachial plexus injuries

A

Damage to the upper trunk (traction between head and shoulder) → Erb palsy (“waiter’s tip”)

Damage to the lower trunk (upward force on arm) → Klumpke palsy (claw hand)

Damage to the long thoracic nerve (axillary node dissection, chest tube insertio) → denervation of serratus anterior → winged scapula

70
Q

MSK nerve injuries to the upper extremities

A

Damage to the radial nerve (mid-shaft humerus fracture) → wrist drop (weak wrist extensors), impaired sensation over lateral dorsum of hand

Damage to the ulnar nerve (damage to medial epicondyle of humerus, hook of the hamate) → “ulnar claw,” atrophy of the hypothenar eminence, weankness of wrist flexion

Damage to the median nerve (compression of carpal tunnel via pregnancy, hypothyroidism, etc.) → pain/paresthesias over palmar aspects of first 3 1/2 digits, thenar atrophy and weakness on thumb abduction/opposition

Damage to the axillary nerve (fracture at the surgical neck of the humerus) → paralysis of deltoid, teres minor

71
Q

Antiphospholipid antibody

A

Associated with SLE and antiphospholipid syndrome which is characterized by hypercoagulability, paradoxical PTT prolongation, and recurrent miscarriages

72
Q

What does the Trendelenberg sign indicate?

A

Trendelenberg sign = hip tilts towards the unsupported leg

It indicates contralateral hip abductor weakness

Hip abductors, the gluteus minimus, gluteum medius, and tensor fascia lata are innervated by the superior gluteal nerve which can be damaged in the superiomedial aspect of the gluteus

73
Q

Musle fiber types

A

Type I (slow twitch) fibers perform actions requiring low-level sustained force (e.g. postural maintenance) and are primarily aerobic (high myoglobin and mitochondria concentrations)

Type IIb (fast twitch) fibers perform rapid forceful pulses of movement derive ATP via anaerobic glycogenolysis and subsequent glycolysis

Type IIa fibers are intermediate between type I and type IIb and generate ATP via aerobic metabolism

74
Q

Fibromyalgia

A

Chronic (> 3 months), widespread MSK pain associated with stiffness, paresthesias, poor sleep, fatigue, pschiatric disturbances likely due to abnormal central processing of painful stimuli

Most commonly seen in females 20-50 y/o

Tx: regular exercise, antidepressants (TCAs, SNRIs), and anticonvulsants

75
Q

Polymyalgia rheumatica

A

Pain and stiffness in the shoulders and hips often with fever, malaise, and weight loss; no muscle weakness

Most common in women > 50 y/o

Labs: ↑ ESR, ↑ CRP, normal CK

Tx: rapid response to low-dose corticosteroids

76
Q

Features of a fat embolism

A

Risk factors: long bone and pelvic fractures, orthopedic procedures

Triad: respiratory distress, neurological symptoms, petechial rash

77
Q

Malignant hyperthermia

A

Autosomal dominant defect in ryanodine receptors that release excessive calcium into muscle cells after exposure to an anesthetic → excess intracelluar calcium stimulated ATP-dependent reuptake by the SR → excessive ATP consumption generates heat which damages muscles

Characterized by fever, muscle rigidity, tachycardia, hypertension, hyperkalemia, myoglobinemia

Tx: dantrolene (inhibits ryanodine receptor preventing further intracellular calcium release)

78
Q

Marfan vs. homocystinuria

A

Features in common: pectus deformity, tall stature, arachnodactyly, joint hyperlaxity, skin hyperelasticity, scoliosis

Marfan (fibrillin-1 gene mutation): AD, normal intellect, aortic root dilation, upward lense dislocation

Homocystinuria (cystathionine-beta-synthase mutation): AR, intellectual disability, thrombosis, downward lens dislocation, megaloblastic anemia, fair complexion

USMLE Step 1 (20 decks)

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