What could be the cause of multiple subcutaneous cysts on the face and arms in a patient for an extended period, such as several months or years?

Multiple Subcutaneous Cysts on Face and Arms: Diagnostic Approach

The most likely diagnosis is epidermoid (epidermal inclusion) cysts, which are the most common benign cutaneous cysts and characteristically present as mobile, flesh-colored nodules with a central punctum containing keratinous material. 1

Primary Differential Diagnoses

Epidermoid Cysts (Most Common)

• Present as mobile, flesh-colored nodules with a characteristic central punctum (dark opening on the surface), distinguishing them from other subcutaneous masses 1, 2
• Contain thick, white-yellow cheesy keratinous material mixed with normal skin flora 1, 2
• Can develop over years without symptoms, then suddenly become inflamed if the cyst wall ruptures 2
• Multiple giant epidermoid cysts on the face and arms have been documented, with sizes ranging from 1-15 cm, developing over decades 3, 4
• Physical examination should specifically assess: presence or absence of central punctum, mobility and consistency of lesions, duration, and any recent changes in character 1

Steatocystoma Multiplex (Rare but Classic Presentation)

• Presents as multiple cysts specifically erupting over the chest, arms, axilla, and neck, matching the distribution described in your question 5
• Cysts occasionally exsanguinate oily material when ruptured 5
• Can occur as spontaneous mutation or inherited in autosomal dominant pattern 5
• Benign condition requiring no treatment unless symptomatic 5

Mastocytomas (If Lesions Appeared in Infancy/Childhood)

• Solitary mastocytomas typically present at birth or within the first week of life, though can develop during first years 6
• Positive Darier's sign (wheal and erythema after gently rubbing the lesion) confirms cutaneous mastocytosis 6
• Associated symptoms include facial flushing, pruritus, and potential for blistering with trauma 6
• Most resolve spontaneously before puberty 6

Critical Red Flags Requiring Biopsy

Consider malignancy and obtain biopsy when: 1

• Chronic lesion unresponsive to standard therapy
• Marked asymmetry or unifocal recurrent lesion
• Loss of normal tissue architecture or focal hair loss
• Rapid growth or ulceration
• Indurated, irregular borders or fixation to underlying structures

Squamous cell carcinoma can arise in chronic cysts, particularly those related to chronic wounds or scars, presenting as indurated nodular keratinizing or crusted tumor that may ulcerate 1

Additional Diagnostic Considerations

Subcutaneous Fungal Cysts

• Should be suspected in all subcutaneous cystic lesions, particularly if non-tender and ranging 3-10 cm in size 7
• Commonly involve hands, forearms, elbows, legs, and feet 7
• All excised tissue should be sent for both culture and histopathology to exclude fungal etiology 7

Paraneoplastic Syndrome

• Multiple recurrent acquired epidermal cysts on face and scalp have been reported as possible paraneoplastic syndrome associated with mycosis fungoides 8
• Consider if patient has concurrent skin conditions or lymphoproliferative disorders 8

Recommended Diagnostic Approach

Initial evaluation should include: 1

1. Detailed physical examination assessing central punctum presence, mobility, consistency, and duration of lesions
2. Assessment for Darier's sign if lesions appeared in childhood (to exclude mastocytosis) 6
3. Family history to identify autosomal dominant inheritance patterns (steatocystoma multiplex) 5

Imaging is indicated when:

• Clinical uncertainty exists based on history or physical characteristics 1
• Lesions are large (>5 cm) or demonstrate atypical features 3, 4
• MRI or ultrasound can differentiate epidermoid cysts from other pathologies 3

Histopathologic evaluation is mandatory when: 1

• Any features suggesting malignancy are present
• Lesions are unresponsive to conservative management
• Clinical diagnosis remains uncertain

Management Pitfalls to Avoid

• Do not misdiagnose as neurofibromatosis based solely on multiple subcutaneous masses without radiologic evaluation and pathologic confirmation 3
• Avoid treating inflamed epidermoid cysts as simple abscesses with antibiotics alone without addressing the cyst wall, which leads to recurrence 1, 2
• Do not assume benignity without proper evaluation, as malignant transformation can occur in chronic cysts 1
• Always send excised tissue for culture and histopathology to exclude fungal etiology, which can masquerade as benign lesions 7