What is the workup for a patient presenting with hyperpigmentation in the axilla (armpit) and neck?

Workup for Hyperpigmentation in the Axilla and Neck

The most appropriate workup for a patient presenting with hyperpigmentation in the axilla and neck should begin with evaluation for acanthosis nigricans, as this is the most common cause of such presentation.

Initial Assessment

• Detailed history focusing on:

  • Onset and progression of hyperpigmentation 1
  • Associated symptoms (pruritus, inflammation) 1
  • Medical history, particularly metabolic disorders, obesity, diabetes 1, 2
  • Medication history (insulin, corticosteroids, niacin, hormonal contraceptives) 1
  • Family history of similar conditions or endocrine disorders 1, 2

• Physical examination should evaluate:

  • Distribution pattern (symmetrical vs. asymmetrical) 1
  • Texture (velvety, rough, smooth) 1, 2
  • Associated features (comedones, papillomatosis) 1, 2
  • Other affected areas (groin, inframammary regions, knuckles) 1, 2
  • Presence of skin tags in affected areas 2

Laboratory Investigations

• Fasting blood glucose and HbA1c 1, 2
• Fasting insulin levels 1, 2
• HOMA-IR (Homeostasis Model Assessment-Insulin Resistance) calculation 2
• Lipid profile 1
• Liver function tests 1
• Thyroid function tests 3

Additional Investigations Based on Clinical Suspicion

• For suspected malignancy-associated acanthosis nigricans:

  • Age-appropriate cancer screening 1, 2
  • Abdominal imaging (ultrasound, CT, or MRI) 1
  • Chest radiography 1

• For suspected syndromic causes:

  • Genetic testing if features of specific syndromes are present 2

Skin Biopsy

• Skin biopsy should be performed if:
  • Diagnosis is uncertain 4
  • Malignancy is suspected 4
  • Atypical features are present 4
  • Differentiation from other pigmentary disorders is needed 4, 5

Differential Diagnosis

• Acanthosis nigricans (most common) 1, 2
• Post-inflammatory hyperpigmentation 6
• Erythrasma (bacterial infection with coral-red fluorescence under Wood's lamp) 3
• Tinea versicolor 6
• Dowling-Degos disease (reticulate pigmentation with comedo-like lesions) 5
• Haber's syndrome 5
• Melasma extending to neck 6
• Drug-induced hyperpigmentation 4

Special Considerations

• Wood's lamp examination can help differentiate epidermal from dermal pigmentation and identify certain infections 3
• In patients with suspected malignancy (rapid onset, extensive involvement, weight loss), more aggressive workup is warranted 1, 2
• Consider referral to endocrinology if metabolic abnormalities are identified 1, 2
• Dermatology referral for atypical presentations or when diagnosis remains uncertain after initial workup 4

Follow-up

• Regular monitoring of metabolic parameters if acanthosis nigricans is diagnosed 1, 2
• Repeat examination for any changes in pigmentation pattern or texture 2
• Treatment of underlying cause when identified 1, 2

Remember that acanthosis nigricans is often a cutaneous marker of insulin resistance and may precede the diagnosis of diabetes or metabolic syndrome, making proper identification and workup essential for overall patient health 1, 2.