Musculoskeletal and skin
Practice questions with explanations

A. Osteoclasts, multinucleated cells that acidify a sealed zone and secrete enzymes to dissolve mineral and matrix

Osteoclasts and osteoblasts work in coupled units so bone is continuously remodelled, and osteoporosis develops when resorption outpaces formation. Bisphosphonates and denosumab suppress osteoclasts, while teriparatide stimulates osteoblasts. Understanding the coupling explains why antiresorptives also eventually reduce formation and why bone turnover markers fall.

C. Protein catabolism causing proximal myopathy, typically affecting shoulder and hip girdle muscles

Glucocorticoids promote breakdown of muscle protein for gluconeogenic substrate, producing proximal weakness that patients notice as difficulty rising from a chair or reaching overhead. It is dose and duration related and improves slowly after reduction. Fluorinated steroids such as dexamethasone appear more likely to cause it than prednisolone.

B. Whether the drug absorbs ultraviolet energy and generates reactive species in skin, producing phototoxic or photoallergic reactions in sun-exposed areas

Phototoxic reactions look like exaggerated sunburn, occur on first exposure and are dose-related, while photoallergic reactions are immune-mediated, appear as eczema and require sensitisation. Doxycycline, amiodarone, quinolones, thiazides, NSAIDs and St John's wort are among the common culprits, and the counselling point is sun protection or avoidance rather than stopping treatment.