Dermatology MCQ - Inflammatory Dermatoses - Erythema gyratum repens

A 68-year-old man with a 40-pack-year smoking history presents with a rapidly progressive, intensely pruritic rash that has developed over the past few weeks. On examination, you find widespread, concentric, wavy bands of erythema with a delicate, trailing scale over much of his trunk, giving a appearance reminiscent of wood grain. The most critical next step in management is:

A. Initiate high-potency topical corticosteroids and oral antihistamines
B. Perform a skin biopsy for routine histology and direct immunofluorescence
C. Order a chest CT scan and begin a thorough investigation for an underlying malignancy
D. Prescribe a course of systemic corticosteroids
E. Order patch testing to identify a contact allergen

Correct Answer: C. Order a chest CT scan and begin a thorough investigation for an underlying malignancy

Answer & Explanation

Explanation:

The description of concentric, wavy, wood-grain-like bands of erythema with trailing scale is pathognomonic for Erythema Gyratum Repens (EGR). EGR is almost universally recognized as a paraneoplastic syndrome.

• Key Diagnostic Clues:

  • Morphology: The "wood grain" or "zebra-like" pattern is unique and highly characteristic.

  • Rapid Evolution: The rash can migrate very quickly, up to 1 cm per day.

  • Intense Pruritus: This is a common and distressing feature.

  • Association: Over 80% of cases are associated with an underlying malignancy. The most common associated cancer is lung cancer, which is strongly suggested by this patient's significant smoking history. Other associated malignancies include breast, esophageal, and gastric cancers.

The other options are incorrect or secondary:

• A. Initiate high-potency topical corticosteroids and oral antihistamines: While this may provide some symptomatic relief for the pruritus, it does not address the underlying, life-threatening cause. The rash is notoriously resistant to treatment unless the malignancy is controlled.

• B. Perform a skin biopsy: A biopsy can be performed and will show a nonspecific superficial perivascular dermatitis with epidermal hyperplasia and scale. However, it is not the most critical step. The diagnosis is primarily clinical, and the urgency lies in identifying the underlying cancer. A biopsy should not delay the oncologic workup.

• D. Prescribe a course of systemic corticosteroids: This is ineffective for controlling EGR and would be dangerous as it could mask symptoms and delay the diagnosis of cancer.

• E. Order patch testing: The presentation is not consistent with a contact dermatitis, which would present with eczematous plaques in areas of contact, not a migratory, wood-grain pattern covering the trunk.

Key Associations for Erythema Gyratum Repens

• Pathophysiology: Considered a classic paraneoplastic phenomenon, likely due to cross-reactivity between tumor antigens and skin antigens or the production of cytokines by the tumor that stimulate the cutaneous inflammatory response.

• Clinical Presentation: The concentric rings migrate rapidly and are often described as having a "timber grain" appearance. Scale is often present just inside the advancing edge ("trailing scale").

• Temporal Relationship: The skin eruption often precedes the diagnosis of cancer by months. In some cases, the rash improves or resolves with successful treatment of the malignancy and recurs if the cancer relapses.

• Differential Diagnosis: Other figurate erythemas, but none have the same rapid migration and dramatic wood-grain pattern. The main differentials are other paraneoplastic dermatoses like necrolytic migratory erythema (associated with glucagonoma).

• Histopathology: Nonspecific. Shows hyperkeratosis, parakeratosis (the scale), and a mild superficial perivascular lymphohistiocytic infiltrate. Eosinophils may be present. There are no specific diagnostic features.

• Prognosis: The prognosis is directly tied to the associated malignancy.

• Management:

  1. Comprehensive Cancer Workup: This is the cornerstone of management. Investigations should include a thorough history and physical, CT chest/abdomen/pelvis, mammography, and other age-appropriate cancer screenings.

  2. Symptomatic Control: Antihistamines and topical corticosteroids can be attempted for pruritus, but response is often poor.

  3. Treat the Malignancy: Effective treatment of the underlying cancer is the only reliable way to clear the eruption.