A 52-year-old man from Delhi presents with progressive darkening and thickening of skin in the neck, axillae, and groin for 6 months. On examination, he has velvety, hyperpigmented plaques with a papillomatous surface. He reports a 10 kg weight loss over the past year and persistent abdominal discomfort. What is the most appropriate next step in management?

Explanation

## Clinical Context This patient presents with acanthosis nigricans (AN) in the setting of constitutional symptoms (weight loss, abdominal discomfort) and metabolic risk factors. The velvety, hyperpigmented, papillomatous appearance is pathognomonic for AN. ## Pathophysiology of Acanthosis Nigricans Acanthosis nigricans is a paraneoplastic syndrome in ~90% of malignancy-associated cases, and an insulin-resistance marker in metabolic cases. The key associations are: | Association | Frequency | Key Feature | |---|---|---| | **Insulin resistance** | 70–80% | Obesity, PCOS, Type 2 DM | | **Malignancy** | 10–30% (varies by age) | Abdominal malignancy (gastric, lung, breast) | | **Medications** | Rare | Oral contraceptives, corticosteroids | **Key Point:** In a patient >50 years with AN and constitutional symptoms (weight loss, abdominal pain), malignancy must be excluded before attributing it to metabolic disease. ## Why Metabolic & Imaging Workup is First-Line 1. **Fasting blood glucose and HbA1c** — Screen for Type 2 DM and insulin resistance, which are present in the majority of AN cases and are modifiable. 2. **Abdominal imaging (CT or ultrasound)** — The combination of AN + weight loss + abdominal discomfort raises suspicion for occult malignancy (gastric cancer is most common in India). Imaging is essential to rule out paraneoplastic AN before attributing findings to metabolic causes alone. **High-Yield:** In patients >40 years with AN and red flags (weight loss, abdominal symptoms, constitutional signs), malignancy screening takes priority over dermatological treatment. **Clinical Pearl:** The presence of tripe palms (velvety thickening of palms) or other paraneoplastic signs (e.g., sudden onset, rapid progression) further raises malignancy risk. ## Algorithm for AN Management ```mermaid flowchart TD A[Acanthosis Nigricans diagnosed]:::outcome --> B{Age and red flags?}:::decision B -->|Age >40, weight loss, abdominal symptoms| C[Metabolic + malignancy screening]:::action B -->|Young, obese, no constitutional symptoms| D[Metabolic screening only]:::action C --> E[FBS, HbA1c, abdominal imaging]:::action D --> F[FBS, HbA1c, lipid profile]:::action E --> G{Malignancy found?}:::decision G -->|Yes| H[Oncology referral]:::urgent G -->|No| I[Manage insulin resistance]:::action I --> J[Weight loss, metformin, topical agents]:::action ``` **Tip:** Skin biopsy is confirmatory but not the first step—it does not change management and delays investigation of systemic disease. [cite:Harrison 21e Ch 52]