Initial Approach to Investigating Acanthosis Nigricans in Primary Care
The initial approach to investigating acanthosis nigricans (AN) in primary care should focus on screening for insulin resistance and associated metabolic disorders, as AN is primarily a cutaneous marker of these underlying conditions.
Clinical Assessment
Physical Examination
- Carefully document the location and severity of AN lesions (typically velvety, hyperpigmented plaques)
- Common locations: nape of neck, axillae, groin, inframammary areas, and flexural surfaces 1
- Assess for obesity by measuring height, weight, and calculating BMI 2
- Complete physical examination to look for other signs of insulin resistance or endocrine disorders:
- Thyroid palpation
- Blood pressure measurement
- Assessment for other skin manifestations (e.g., lipodystrophy) 2
History Taking
- Family history of type 2 diabetes, cardiovascular disease, or metabolic syndrome
- Personal history of weight changes, menstrual irregularities (in females), or symptoms of diabetes
- Medication history (some medications can cause AN)
- Assessment for symptoms suggesting malignancy (unexplained weight loss, anorexia, fatigue)
Laboratory Investigations
First-Line Tests
- Fasting plasma glucose 2
- Hemoglobin A1C
- Lipid profile (total cholesterol, LDL, HDL, triglycerides) 2
- Liver function tests 2
- Homeostasis Model Assessment-Insulin Resistance (HOMA-IR) calculation 3
- Requires fasting insulin and glucose levels
- HOMA-IR > 2.5 is significant for insulin resistance 3
Additional Tests Based on Clinical Suspicion
- Thyroid-stimulating hormone (TSH) 2
- For females with irregular periods or signs of hyperandrogenism:
- Free testosterone
- DHEAS (Dehydroepiandrosterone sulfate)
- 17-OH progesterone 4
Risk Stratification
High-Risk Factors Requiring More Comprehensive Evaluation
- Presence of multiple risk factors:
- Overweight/obesity
- Family history of type 2 diabetes
- High-risk ethnicity (American Indian, African American, Hispanic, Asian/Pacific Islander)
- Signs of other conditions associated with insulin resistance (hypertension, dyslipidemia, polycystic ovary syndrome) 2
Warning Signs for Malignancy-Associated AN
- Rapid onset
- Extensive involvement
- Unusual locations (e.g., oral mucosa)
- Absence of obesity or other risk factors for insulin resistance
- Unexplained weight loss 5
Referral Criteria
When to Refer to Secondary Care
- Suspected malignancy-associated AN
- Extensive or treatment-resistant AN
- Confirmed insulin resistance with poor response to lifestyle modifications
- Suspected syndromic AN (associated with genetic syndromes)
- Diagnostic uncertainty 2
Imaging Considerations
- Routine imaging is not recommended for typical AN associated with obesity/insulin resistance
- Consider imaging studies only when malignancy is suspected:
- CT scan of chest, abdomen, and pelvis may be appropriate
- PET/CT is not recommended for routine screening but may be warranted in specific situations 2
Management Approach
Initial Management in Primary Care
- Address underlying insulin resistance through:
- Weight reduction (most effective strategy) 1
- Increased physical activity
- Dietary modifications
- Monitor for development of diabetes and other metabolic complications
- Educate patients about the relationship between AN and metabolic disorders
Common Pitfalls to Avoid
- Treating AN as merely a cosmetic issue without investigating underlying metabolic disorders
- Failing to calculate HOMA-IR, which is a good tool for assessment of insulin resistance 1
- Missing malignancy-associated AN by assuming all cases are related to obesity/insulin resistance
- Ordering unnecessary extensive imaging studies for typical obesity-associated AN
- Neglecting patient education about the significance of AN as a marker for metabolic disorders
By following this structured approach to investigating acanthosis nigricans, primary care providers can effectively identify underlying metabolic disorders and initiate appropriate management or referral.