MSK & CTD - Diseases

Question 1

Basal Cell Carcinoma

Answer 1

Most common skin cancer; commonly found in sun-exposed areas; locally invasive but almost never metastasizes

Presents as pink, pearly nodules with rolled borders, often with telangiectasias and central ulceration; may also present as a scaly plaque

Histology: Nests of basaloid cells within the dermis

Treatment: 5-fluorouracil

Question 2

Squamous Cell Carcinoma

Answer 2

Second most common type of skin cancer; commonly found on face, lips, ears, and hands; locally invasive, may occasionally spread to lymph nodes and metastasize

Presents as ulcerative, red, scaly lesions

Question 3

Actinic Keratoses

Answer 3

Rough, erythematous or brownish plaques or papules

Results from sun exposure; precursor lesion to squamous cell carcinoma of the skin

Question 4

Keratoacanthoma

Answer 4

A variant of squamous cell carcinoma of the skin

Grows rapidly over 4-6 weeks and may regress spontaneously over the course of months

Question 5

Melanoma

Answer 5

Arises out of dysplastic nevi; watch out for ABCDEs:

Asymmetry
Irregular Borders
Color variation 
Diameter > 6 mm 
Evolution over time 

Risk: Sun exposure, fair skin coloration

Treatment: Excision; Vemurafenib (Braf kinase inhibitor) for unresectable tumors

Question 6

Osteopetrosis

Answer 6

Caused by a mutation in Carbonic Anhydrase in osteoclasts, resulting in an inability of the osteoclast to generate a sufficiently acidic environment necessary for bone resorption

Unchecked bone growth deposited by osteoblasts invade the marrow space causing pancytopenia and extra-medullary hematopoeisis; may result in cranial n. impingement due to narrowing of skull foramina

Causes dense, brittle bones prone to fracture

Labs generally normal but low Ca2+ seen in severe disease

X-ray shows “bone-in-bone” appearance

Question 7

Impetigo

Answer 7

Superficial infection of the skin, most often caused by Strep. pyogenes (“bullous” impetigo is more often caused by S. aureus)

Presents as grouped vesicular lesions on the face of a young child which progress to a “honey-colored” crust

Question 8

Tinea versicolor

Answer 8

Caused by Malassezia furfur fungus; produces an acid that destroys melanocytes, causing hypopigmented lesions; most commonly seen in hot/humid environments

Dx: KOH stain shows characteristic spores with “spaghetti and meatballs” morphology

Treated with topical Miconazole

Question 9

Pemphigoid vulgaris

Answer 9

Caused by autoimmune IgG against desmosomes that anchor epidermal keratinocytes to each other

Presents as flaccid bullae which rupture easily, leaving large areas of denuded skin vulnerable to secondary bacterial infection; often involves oral mucosa

Immunofluoresence shows antibody deposited around keratinocytes in a “reticular” (net-like) pattern; + Nikolsky sign

Treated with corticosteroids

Question 10

Bullous pemphigoid

Answer 10

Caused by autoimmune IgG against hemidesmosomes at the epidermal-dermal junction

Presents as tense bullae with sparing of oral mucosa

IF shows linear deposition of IgG at the epidermal-dermal junction along the basement membrane; Nikolsky sign negative

Question 11

Paget’s Disease of Bone

Answer 11

Localized disorder of bone remodeling; characterized by increases in both osteoblast and osteoclast activity

Presents with increased hat size (thickening of calvarium), hearing loss (narrowing of auditory canal)

Findings: Ca, phosphorous, PTH levels all normal; elevated ALP

Increased risk of osteogenic sarcoma, CHF

Question 12

Osteitis Fibrosa Cystica

Answer 12

Development of cystic bone spaces due to primary hyperparathyroidism resulting in increased bone resorption

Findings: Elevated Ca2+, low phosphorous, high PTH, high ALP

X-ray shows cystic bone spaces filled with brown fibrous tissue (“brown tumor”)

Question 13

Avascular necrosis of the femoral head

Answer 13

Occurs as a side effect of chronic corticosteroid use

Presents with isolated limp and hip pain in the absence of other pathology