Why does multiple sclerosis manifest as asymmetrical and in different parts of the body?

Correct Answer: C

Rationale: Multiple sclerosis is characterized by the immune system mistakenly attacking the myelin sheath in the central nervous system. This results in the formation of lesions that can occur in different parts of the central nervous system, leading to varied symptoms depending on the location of the damage. Choice A is the correct answer because it accurately describes the pathophysiology of multiple sclerosis. Choices B, C, and D are incorrect because they describe mechanisms or locations that are not associated with the pathogenesis of multiple sclerosis.

Correct Answer: A

Rationale: In this scenario, the correct answer is the 55-year-old man with new onset headaches that worsen at night and reported mood swings according to his family. These symptoms, especially when combined with nighttime worsening and mood changes, could indicate a serious underlying disorder such as a brain tumor or increased intracranial pressure. Choice B is incorrect as the unilateral throbbing headache with photophobia and nausea is suggestive of migraine headaches, which are usually not associated with serious underlying disorders. Choice C describes symptoms that are more indicative of tension-type headaches rather than a serious underlying disorder. Choice D presents symptoms that are more likely related to hormonal changes and migraines rather than a serious underlying disorder.

Correct Answer: D

Rationale: The correct answer is 'chronic gout.' Chronic gout is characterized by the presence of tophi, which are large, hard nodules that can develop around joints like toes and elbows. These tophi are a sign of longstanding, untreated gout. Choice A, 'asymptomatic,' is incorrect as the presence of tophi indicates a symptomatic phase. Choice B, 'acute flare,' is incorrect as acute flares are characterized by sudden and severe pain, inflammation, and redness in the joints, not the development of tophi. Choice C, 'the intercritical period,' is also incorrect as this phase occurs between acute attacks and is typically asymptomatic, without the presence of tophi.

Correct Answer: B

Rationale: Muscular dystrophy is primarily caused by mutations in the gene that provides instructions for making the protein dystrophin. Dystrophin plays a crucial role in maintaining the structure of muscle fibers. Glycoprotein is a general term for proteins with sugar molecules attached, not specifically related to muscular dystrophy. Troponin is a protein involved in muscle contraction regulation, and actinomyosin is not a specific muscle protein but a complex formed during muscle contraction. Therefore, the correct answer is dystrophin.

Correct Answer: C

Rationale: Osteosarcoma is an aggressive bone tumor that most commonly arises in the bone marrow of long bones, such as the femur or tibia. Choice A is incorrect as osteosarcoma is not a slow-growing tumor but rather a fast-growing one. Choice B is incorrect as osteosarcoma is not typically solitary but can involve multiple lesions. Choice D is incorrect as osteosarcoma primarily affects the medullary (marrow) cavity of bones, rather than infiltrating the trabeculae in spongy bone and surrounding tissue.