What is the recommended course of action for a 24-year-old male with a newly noticed, asymptomatic, dark pigmented patch on the posterior neck, resembling a birthmark, with no recall of its presence by the patient or their spouse?

Evaluation of a Newly Noticed Dark Pigmented Patch on the Posterior Neck

This patient requires dermatologic evaluation with full-thickness excisional biopsy of the lesion to definitively rule out melanoma, as any newly noticed pigmented lesion with uncertain duration and change in appearance warrants histopathologic examination.

Initial Assessment and Risk Stratification

The clinical presentation raises concern for several reasons that require immediate attention:

• The lesion is newly noticed with uncertain duration, which meets criteria for suspicious pigmented lesions requiring evaluation 1, 2
• Progressive change or new appearance of a pigmented lesion is a major warning sign that mandates referral or excision to exclude melanoma 1
• The patient's age (24 years) does not exclude malignancy, as melanoma can occur in young adults 3
• Changes in symmetry, border, color, or diameter of pigmented lesions may suggest melanoma or other cutaneous malignancy 3

Recommended Diagnostic Approach

Physical Examination Requirements

Perform a comprehensive skin examination including:

• Complete examination of the entire skin surface including scalp to detect additional primary melanomas or suspicious lesions 3, 1
• Inspection of the face, scalp, and neck for ulcerations or other pigmented lesions 3
• Examination of all regional lymph nodes (cervical, preauricular, supraclavicular) as regional lymph node enlargement is highly suggestive of melanoma with nodal metastasis 1
• Assessment of the lesion for ulceration, which increases malignancy risk 3

Definitive Diagnostic Procedure

Full-thickness excisional biopsy is the standard of care for any suspected melanocytic malignancy:

• Excise the entire lesion with a 2-5 mm margin of normal skin laterally and include subcutaneous fat 3, 1
• This allows confirmation of diagnosis and accurate Breslow thickness measurement for staging 3
• Shave biopsies and punch biopsies are contraindicated as they make pathological staging impossible 3
• Use a surgical knife rather than laser or electrocoagulation to avoid tissue destruction that interferes with histologic assessment 1

Critical Pitfalls to Avoid

• Do not assume this is a benign birthmark based solely on appearance, as the uncertain timeline and lack of prior documentation are concerning 1, 2
• Do not perform partial biopsy or incisional biopsy in primary care settings 3
• Do not delay evaluation waiting for the lesion to change further, as early diagnosis significantly impacts prognosis 3, 1
• Prophylactic excision of small congenital nevi without suspicious features is not recommended, but this lesion has suspicious features (newly noticed, uncertain duration) 3

Differential Considerations

While the differential includes benign entities such as:

• Nevus spilus (speckled lentiginous nevus) which can be acquired 4
• Hypermelanotic nevus (dark brown to black macules/papules, most common on back) 5
• Blue nevus (dermal melanocytes presenting as pigmented lesions) 6

The key distinguishing feature requiring action is the newly noticed nature and uncertain timeline, which overrides benign appearance and mandates histopathologic diagnosis 1, 2.

Required Histopathology Reporting

The pathology report must include 3, 1:

• Confirmation of melanocytic nature and malignancy status
• Breslow thickness (measured to nearest 0.1 mm from granular layer to tumor base)
• Clark level of invasion
• Presence or absence of ulceration
• Assessment of completeness of excision with margin measurements
• Mitotic rate, regression, and lymphocytic infiltrate

Follow-up Based on Histopathology

If melanoma is confirmed, the Breslow index is the most powerful prognostic factor and will guide further management including consideration of sentinel lymph node biopsy and imaging 3, 1.