What are the possible causes and treatments for hyperpigmented flat lesions on the skin?

Hyperpigmented Flat Lesions: Causes and Management

For hyperpigmented flat lesions, the primary diagnostic approach is complete excisional biopsy with a 2-5 mm margin when melanoma is suspected, while benign conditions like postinflammatory hyperpigmentation, melasma, solar lentigines, and café-au-lait macules can be managed with topical agents, chemical peels, cryotherapy, or laser therapy. 1, 2

Diagnostic Approach

Initial Clinical Assessment

Evaluate all hyperpigmented flat lesions using the ABCDE criteria to exclude melanoma: 3

• Asymmetry of the lesion
• Borders that are irregular
• Color heterogeneity
• Diameter >7 mm
• Evolution (recent changes in size, color, or shape)

Document the duration, changes over time, symptoms, exact anatomic site, size, and detailed description including irregular margins and pigmentation patterns. 4

When to Perform Excisional Biopsy

Any flat pigmented lesion with suspicious features requires urgent referral and complete excisional biopsy rather than punch biopsy. 4, 5 This is critical because:

• Punch biopsies prevent accurate pathological staging and risk misdiagnosis from partial sampling 5
• Maximum tumor thickness cannot be assessed, making it impossible to determine appropriate excision margins 5
• Partial sampling risks missing the thickest portion of the lesion, leading to understaging 5

Perform a full-thickness elliptical excision including the entire lesion with a 2-5 mm clinical margin of normal skin laterally and subcutaneous fat deep to the lesion, using a scalpel to avoid tissue destruction. 5, 3

Common Benign Causes

Postinflammatory Hyperpigmentation

The most common cause of acquired hyperpigmentation, occurring after inflammatory skin conditions or trauma. 1, 2

Melasma

Symmetric hyperpigmentation typically on sun-exposed facial areas, influenced by hormonal factors and UV exposure. 1, 2, 6

Solar Lentigines

Flat, well-demarcated brown macules on chronically sun-exposed skin in middle-aged and elderly individuals. 1, 2

Café-au-Lait Macules

Uniformly pigmented flat lesions that are generally benign when isolated, though multiple lesions may indicate systemic conditions. 3, 1, 2

Ephelides (Freckles)

Small, light brown macules that darken with sun exposure. 1, 2

Special Consideration: Lentigo Maligna

Lentigo maligna represents melanoma in situ, appearing as a flat pigmented lesion commonly on sun-exposed facial areas in older individuals. 4, 3

Complete excision is the preferred treatment due to risk of invasive transformation, though the progression risk is poorly established and may be unlikely within the lifespan of very elderly patients. 3 For elderly patients where complete excision is impossible or contraindicated, alternative options include radiotherapy, cryotherapy, or observation only, though recurrence risk is higher than with surgery. 3, 4

Treatment Options for Benign Lesions

First-Line Topical Therapy

Hydroquinone is the gold standard topical treatment, used alone or in combination with other agents. 6 Additional topical options include retinoids, corticosteroids, and azelaic acid. 2

Photoprotection with broad-spectrum sunscreens protective against both UV and visible light is recommended for all patients with hyperpigmentation. 6

Procedural Interventions

Chemical peels, cryotherapy, and laser or light-based therapies are effective adjunctive treatments. 1, 2 However, caution is required in patients with richly pigmented skin due to increased risk of postinflammatory hyperpigmentation. 6

For café-au-lait macules desiring treatment, surgical excision or laser therapy are options. 1, 2

Cryotherapy Technique

When using cryotherapy for appropriate lesions, apply liquid nitrogen for 15-20 seconds until 1-2 mm of circumferential skin appears frozen, thaw for 20-60 seconds, then repeat the freeze step at 3-week intervals. 3 Avoid cryotherapy on eyelids, lips, nose, and ears. 3

Critical Pitfalls to Avoid

• Never perform punch biopsy on suspected melanoma - this prevents accurate staging and risks understaging the lesion 5
• Do not use tissue-destructive methods (laser, electrocautery) for initial diagnosis - this compromises histological assessment 3
• Avoid frozen sections for pigmented lesions - standard histological examination is required 3
• Exercise extreme caution with procedural treatments in darker skin types due to higher risk of postinflammatory hyperpigmentation 6
• Document the reason clearly if choosing non-surgical management for lentigo maligna 3