What is Acanthosis Nigricans?

Acanthosis Nigricans (AN) is a skin condition characterized by dark, thick, velvety patches of skin, typically in body folds and creases. It is most commonly a sign of insulin resistance and is strongly associated with obesity, prediabetes, diabetes, and metabolic syndrome.

What Does it Look Like?

• Color: Dark brown, gray, or black hyperpigmentation
• Texture: Thick, velvety, or "velvety-smooth" feel
• Common Locations:
  • Neck (most common)
  • Armpits (axillae)
  • Groin
  • Knuckles, elbows, knees
  • Under breasts, belly button
• Symmetrical: Affects both sides of body equally

Types/Causes:

1. Benign (Insulin Resistance-Related)—MOST COMMON (>90%):

• Obesity: Especially in children, adolescents, young adults
• Prediabetes, Type 2 Diabetes
• Metabolic Syndrome
• Polycystic Ovary Syndrome (PCOS)
• Cushing's Syndrome (Excess Cortisol)
• Acromegaly (Excess Growth Hormone)

2. Genetic/Familial:

• Rare inherited forms (autosomal dominant)
• No underlying metabolic disorder

3. Malignancy-Associated (Rare but Serious):

• Gastric Adenocarcinoma (Most Common Cancer)
• Lung, colon, breast, ovarian, lymphoma
• Features Suggesting Malignancy:
  • Sudden, rapid onset in older adult
  • Widespread, severe AN
  • Involves palms, soles, mucous membranes
  • Unexplained weight loss, fatigue, other symptoms

4. Drug-Induced:

• Nicotinic acid (niacin)
• Oral contraceptives
• Corticosteroids
• Growth hormone
• Insulin (high doses)

Why Does Insulin Resistance Cause AN?

• High Insulin Levels: Insulin resistance → body produces excess insulin
• Skin Cell Stimulation: High insulin binds to insulin-like growth factor (IGF) receptors on skin cells → stimulates keratinocyte and fibroblast proliferation → thickened, darkened skin

Symptoms:

• Dark, velvety skin patches (asymptomatic—doesn't hurt or itch usually)
• Occasionally mild itching
• Skin may have odor (from moisture/bacteria in folds)
• Associated symptoms of underlying condition (fatigue, increased thirst/urination if diabetic)

Diagnosis:

Clinical Diagnosis (Visual Inspection):

• Typical appearance + distribution is diagnostic
• Skin biopsy rarely needed (only if malignancy suspected)

Evaluate for Underlying Cause:

• Fasting Glucose, HbA1c: Screen for prediabetes/diabetes
• Fasting Insulin: Assess insulin resistance (often very high)
• Lipid Panel: Check for dyslipidemia (part of metabolic syndrome)
• Thyroid Function (TSH): Rule out hypothyroidism
• If PCOS Suspected: Testosterone, LH, FSH
• If Cushing's Suspected: 24-hour urine cortisol, dexamethasone suppression test
• If Malignancy Suspected: Age-appropriate cancer screening (colonoscopy, upper endoscopy, CT imaging)

Treatment:

1. Treat Underlying Cause (MOST IMPORTANT):

For Insulin Resistance/Obesity:

• Weight Loss: Often leads to significant improvement or complete resolution of AN
• Diet: Low-glycemic, reduced refined carbs/sugars
• Exercise: Improves insulin sensitivity
• Metformin: Improves insulin resistance; may improve AN over months
• GLP-1 Agonists: For weight loss and glucose control
• Bariatric Surgery: For severe obesity—dramatic improvement in AN post-surgery

For Diabetes:

• Optimize blood sugar control

For PCOS:

• Weight loss, metformin, oral contraceptives

For Malignancy:

• Treat cancer—AN often resolves if cancer treated successfully

For Drug-Induced:

• Discontinue offending medication if possible

2. Cosmetic Treatments (Improve Appearance but Don't Address Underlying Cause):

• Topical Retinoids (Tretinoin, Adapalene): Promote skin cell turnover; may lighten pigmentation over time
• Topical Keratolytics: Salicylic acid, alpha-hydroxy acids, urea—reduce thickness
• Laser Therapy: Q-switched or fractional lasers—reduce pigmentation (expensive, multiple sessions)
• Chemical Peels
• Note: These treatments provide only modest, temporary improvement; AN will return if insulin resistance not addressed

3. Skin Care:

• Keep affected areas clean and dry
• Moisturize to prevent cracking
• Avoid harsh scrubbing (won't "remove" the discoloration)

Prognosis:

• Insulin Resistance-Related AN: Improves significantly or resolves with weight loss and improved metabolic control
• Cosmetic treatments provide only modest benefit if underlying cause not addressed
• Malignancy-associated AN: Prognosis depends on cancer type and stage

Prevention:

• Maintain healthy weight
• Prevent or delay type 2 diabetes (exercise, healthy diet)
• Early treatment of prediabetes/metabolic syndrome