What could be the cause of a yellow patch on the skin over the left shoulder that has been asymptomatic for 3 weeks with no changes, similar to a rash that occurred a few months ago and spontaneously resolved?

Asymptomatic Yellow Patch on Shoulder: Likely Diagnosis and Management

This presentation is most consistent with xanthelasma or xanthoma, a benign lipid deposit in the skin that characteristically appears as a yellow patch, remains asymptomatic, and can spontaneously resolve or recur over months. 1

Clinical Reasoning

The key features pointing toward this diagnosis include:

• Yellow coloration - This is pathognomonic for lipid deposition in the skin, distinguishing it from inflammatory dermatoses which typically present with erythema or other color changes 1
• Asymptomatic nature - The complete absence of pruritus, pain, or other symptoms rules out most inflammatory and infectious etiologies 2, 1
• Chronicity without change - Three weeks of stability without progression suggests a non-infectious, non-inflammatory process 3
• Spontaneous resolution previously - This pattern of self-limited episodes is characteristic of benign lipid deposits rather than progressive conditions 1

Differential Considerations

While xanthoma is most likely, other possibilities to consider include:

• Seborrheic keratosis - Can appear yellowish but typically has a "stuck-on" appearance and waxy texture 3
• Lipoma - Presents as a subcutaneous nodule rather than a flat patch 3
• Post-inflammatory hyperpigmentation - Would not typically appear yellow 2

The absence of new medications makes drug-induced reactions (which can present with yellow discoloration in rare cases) extremely unlikely 2

Recommended Evaluation

A complete skin examination should be performed to identify additional lesions and assess for signs of systemic disease. 4 This is critical because:

• Complete skin examination identifies additional diagnoses in 15% of patients that would otherwise be missed 4
• Multiple xanthomas may indicate underlying lipid disorders requiring treatment 1

Laboratory evaluation should include a lipid panel (total cholesterol, LDL, HDL, triglycerides) to screen for dyslipidemia. 1 While isolated xanthomas can occur without systemic disease, they may be the first manifestation of hyperlipidemia requiring intervention.

If the diagnosis remains uncertain after clinical examination, consider dermatology referral for potential biopsy. 3, 4 Biopsy would show lipid-laden histiocytes confirming the diagnosis, though this is rarely necessary for typical presentations.

Management Approach

Observation is appropriate for asymptomatic lesions, with reassessment in 2-4 weeks to document stability. 1 Given the previous spontaneous resolution, watchful waiting is reasonable.

If lipid abnormalities are identified, treat the underlying dyslipidemia according to cardiovascular risk stratification. 1 This may lead to regression of the cutaneous lesions.

Dermatology referral is indicated if: 1, 3

• The lesion changes in size, color, or becomes symptomatic
• Multiple lesions develop
• Diagnosis remains uncertain after initial evaluation
• Patient desires cosmetic removal

Critical Pitfalls to Avoid

• Do not assume all yellow patches are benign - While xanthoma is most likely, rare presentations of cutaneous lymphoma or other malignancies can have atypical coloration 1
• Do not overlook systemic evaluation - Xanthomas may be the presenting sign of familial hyperlipidemia or secondary dyslipidemia from diabetes, hypothyroidism, or liver disease 1
• Do not delay hematological workup if other symptoms develop - Polycythemia vera can present with skin manifestations, though typically with aquagenic symptoms rather than isolated yellow patches 1, 5