Musculoskeletal, Skin & Connective Tissue

Rheumatology, bone pathology, dermatology and upper- and lower-limb nerve injuries.

Exam weight 6–8% · 2 QBank items · 4 flashcards

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Rheumatology

Rheumatoid arthritis: symmetric small-joint involvement, morning stiffness over an hour, anti-CCP is most specific, pannus erodes bone.
Osteoarthritis: asymmetric, worse with use, Heberden and Bouchard nodes, osteophytes and joint-space narrowing.
Gout: negatively birefringent needle-shaped urate crystals (yellow when parallel); pseudogout has positively birefringent rhomboids.
SLE: ANA sensitive, anti-dsDNA and anti-Smith specific; antiphospholipid antibodies cause thrombosis with a paradoxically prolonged PTT.

Osteoporosis: normal labs with low bone density; osteomalacia: low calcium and phosphate with high alkaline phosphatase and PTH.
Paget disease of bone: isolated high alkaline phosphatase, mosaic lamellar bone, high-output heart failure, hearing loss.
Osteosarcoma: metaphysis of long bones in adolescents, Codman triangle and sunburst pattern.
Ewing sarcoma: t(11;22), diaphysis, onion-skin periosteal reaction, small round blue cells.

Axillary nerve injury with surgical neck humerus fracture: deltoid weakness and loss of sensation over the lateral shoulder.
Radial nerve injury with midshaft humerus fracture: wrist drop and loss of the dorsal hand web sensation.
Common peroneal injury at the fibular neck: foot drop with loss of eversion and dorsiflexion — 'PED'.
Erb palsy (C5–C6) gives waiter's tip; Klumpke (C8–T1) gives a claw hand.

Psoriasis: silvery scaling on extensor surfaces, Auspitz sign, parakeratosis and acanthosis.
Pemphigus vulgaris: intraepidermal, positive Nikolsky, anti-desmoglein, net-like IgF on immunofluorescence; bullous pemphigoid is subepidermal and Nikolsky negative.
Basal cell carcinoma: pearly papule with rolled borders and telangiectasias, palisading nuclei; rarely metastasises.
Melanoma: depth of invasion (Breslow) drives prognosis; BRAF V600E mutation guides vemurafenib.