A patient presents with multiple, hyperpigmented, velvety plaques in flexural areas such as the axillae and neck. The lesions are associated with obesity and insulin resistance. Which of the following conditions is most likely responsible for this presentation?

Correct Answer: A

Rationale: Acanthosis nigricans is a skin condition characterized by multiple, hyperpigmented, velvety plaques typically seen in flexural areas such as the axillae, neck, and groin. These lesions are often associated with obesity and insulin resistance. The appearance of acanthosis nigricans is distinct from other skin conditions such as seborrheic keratosis, dermatofibroma, and epidermal nevus. Acanthosis nigricans is commonly seen in conditions like obesity, type 2 diabetes, and metabolic syndrome due to the insulin resistance that leads to the overgrowth of keratinocytes.

Correct Answer: D

Rationale: Papillary thyroid carcinoma is the most common type of thyroid cancer and is known for presenting as a painless unilateral enlargement of the thyroid gland. Fine-needle aspiration cytology typically reveals classic features such as numerous microfollicles and psammoma bodies. Thyroglossal duct cyst, Hashimoto's thyroiditis, and thyroid adenoma would not typically present with these cytological features or with painless thyroid enlargement as seen in papillary thyroid carcinoma.

Correct Answer: D

Rationale: The presentation described is characteristic of a parathyroid adenoma. Parathyroid adenomas are benign neoplasms that can present as painless, well-defined nodules usually located in the lower pole of the thyroid gland or in close proximity, such as the lateral aspect of the neck above the clavicle. Fine-needle aspiration cytology of a parathyroid adenoma typically reveals polygonal cells with abundant granular cytoplasm, often referred to as chief cells. This is key in differentiating it from other conditions mentioned in the question.

Correct Answer: C

Rationale: The description provided is classical for fungal keratitis. Fungal keratitis typically presents with a yellowish-white spot on the cornea, often surrounded by a ring of inflammation. Branching, filamentous opacities extending from the corneal lesion are commonly seen on slit-lamp examination in cases of fungal keratitis. This condition is often associated with risk factors such as trauma with organic material or contact lens wear. Prompt diagnosis and treatment with antifungal agents are crucial in managing fungal keratitis to prevent potential complications.

Correct Answer: A

Rationale: The presentation described in the question is most consistent with anterior uveitis. Anterior uveitis, also known as iritis, is characterized by redness, pain, and photophobia in the affected eye. Slit-lamp examination typically reveals ciliary injection (reddening of the conjunctiva and episclera), corneal edema, and a mid-dilated pupil with a fixed reaction to light (miosis). This occurs due to inflammation within the anterior chamber of the eye involving the iris and ciliary body.