Case 1 Discussion

1) What is your Differential Diagnosis (please include the reason for listing each diagnosis)?

The primary skin lesion is a reticulate hyperpigmented patch/plaque. The differential diagnosis is listed below:

  1. Confluent and reticulated papillomatosis (fits primary lesion, distribution, and age of onset. Inframammary location is classic)
  2. Tinea versicolor (also fits primary lesion, distribution, and age of onset)
  3. Acanthosis nigricans (also fits primary lesion, distribution, and age of onset)
  4. Dowling-Degos syndrome (can look very similar to acanthosis nigricans)
  5. Dyskeratosis congenita (fits primary lesion, distribution, and age of onset)
  6. Erythema ab igne (fits primary lesion, distribution)
  7. Drug-induced pigmentation (may present with reticulate pattern lesions)
  8. Sarcoid (may present wtih reticulate pattern lesions)
  9. Mycosis fungoides (may present wit reticulate pattern lesions)
  10. Reticulated erythema mucinosis (fits primary lesion)

2) Would you order any tests?

KOH is an easy non-invasive test useful to confirm tinea versicolor. KOH was negative in this case. Biopsy is a reasonable test to consider. After discussion with patient, a therapeutic trialwas agreed upon and biopsy was deferred.

3) What would be your initial treatment plan?

Treatment: Minocycline 100 mg BID for 6 weeks was recommended.

Course: Patient was 100% clear at 2 month follow-up and remained clear for two years in follow-up. She reported significant improvement in her social life.

4) Summarize your most likely diagnosis

Confluent and reticulate papillomatosis (CARP) was originally described by Gougerot and Carteaud in 1927. It is an uncommon skin condition characterized by hyperpigmented, hyperkeratotic papules and plaques, often with a reticulated pattern. The most affected areas includes anterior torso, particularly the inframammary and midsternal regions, but also include the back, axillae, neck, and face. The onset is often after puberty with a slight preponderance for women. The etiology is unknown. Some theories include a disorder of keratinization, endocrine disorder, fungal infection, or bacterial infection. A recent study isolated an Actinomyces strain with sensitivity to the tetracycline antibiotic family, further substantiating clinical findings of why patients do well on minocyline therapy. The course is often chronic with chances of recurrence; however, CARP is self-limited and treatment is usually for cosmetic reasons. Patients often respond well to minocycline therapy.  

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