Q5: June 2019 PLAB 1 Exam Style Question
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A 29-year-old man with a body mass index (BMI) of 41 kg/m^2 consults his primary care physician, complaining about skin changes in both his axillae and the nape of his neck. He reports that the skin feels thicker and the pigmentation has darkened over the past six months. He has no history of diabetes, hypertension, or endocrine disorders. Upon further questioning, he denies any other symptoms and appears otherwise well. Vital signs reveal a blood pressure of 130/80 mmHg. Physical examination shows thickened, brownish-black, velvety patches in the axillary and nuchal regions. Blood tests including fasting glucose, thyroid function tests, and adrenal function tests are pending.
What is the most likely diagnosis?
A. Tinea corporis
B. Acanthosis nigricans
C. Seborrheic dermatitis
D. Vitiligo
E. Cushing's syndrome
Answer: B. Acanthosis nigricans
Explanation
Background:
The patient is a 29-year-old obese male with a BMI of 41 kg/m^2, presenting with specific skin changes described as brownish-black, velvety plaques located in his axillary and nuchal regions.
Diagnosis Differentiation:
A. Tinea corporis: This would generally present as a ring-like rash with clearer skin in the center and would be pruritic (itchy). It also doesn't usually have the velvety texture described in this case
B. Acanthosis nigricans (AN): This condition presents with the brown, velvety patches of skin usually in areas of body folds like the axilla or back of the neck. It's most commonly linked to obesity and insulin resistance.
C. Seborrheic dermatitis: Generally affects the scalp, face, and torso and would present with flaky, dandruff-like scales and erythematous patches but not the velvety texture described here.
D. Vitiligo: This would manifest as patches of depigmented skin and wouldn't present as darkened, velvety patches.
E. Cushing's syndrome: While Cushing's could be associated with obesity, it usually has a wide range of other symptoms such as 'moon face,' 'buffalo hump,' and purple striae, which are not present in this case.
Reasoning:
Acanthosis nigricans is primarily a cutaneous sign of underlying conditions, most commonly obesity and insulin resistance. Given this patient's elevated BMI, the presentation is highly suggestive of obesity-associated acanthosis nigricans.
Management and Further Evaluation:
This patient should have further evaluation for insulin resistance and associated conditions like type 2 diabetes mellitus. Lifestyle modifications, including weight loss, should be the first step in management. In rare cases, AN can be a paraneoplastic syndrome linked to underlying malignancy, so ruling out other potential underlying causes is also crucial.
Summary
This patient's skin changes and the high BMI make obesity-associated acanthosis nigricans the most likely diagnosis. Further evaluation should include tests for insulin resistance and lifestyle modification is usually the first step in management.
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Reference:
The Primary Care Dermatology Society provides a comprehensive overview of the condition, including its aetiology, history, clinical findings, investigations, and management. It also includes images of typical cases and differential diagnoses.
The NHS offers a brief summary of the condition, its symptoms, causes, diagnosis, and treatment. It also advises when to see a GP and what to expect at the appointment.
Healthline provides an article that explains what acanthosis nigricans is, what causes it, how it’s diagnosed, and how it’s treated. It also includes pictures of the condition and some tips for prevention.
Diabetes.co.uk gives information on the link between acanthosis nigricans and diabetes, as well as the risk factors, symptoms, diagnosis, and treatment of the condition. It also suggests some lifestyle changes that can help improve the skin appearance.
