Differential Diagnosis for the 17-year-old Boy with a Rash
The patient's presentation of multiple hypopigmented macules coalescing into patches, particularly after using a new sunscreen and swimming in a chlorinated pool, suggests several potential diagnoses. The following categories outline the differential diagnosis:
- Single most likely diagnosis
- Pityriasis Versicolor (Tinea Versicolor): This condition is characterized by hypopigmented or hyperpigmented macules that can coalesce into patches, often with fine scaling. The distribution over the upper chest, shoulders, and back, along with the history of recent sunscreen use and swimming, supports this diagnosis. Pityriasis versicolor is caused by a yeast infection and is more common in warm, humid environments.
- Other Likely diagnoses
- Contact Dermatitis: Given the recent introduction of a new sunscreen, contact dermatitis is a possible diagnosis. However, the lack of significant inflammation and the specific pattern of hypopigmentation make it less likely than pityriasis versicolor.
- Seborrheic Dermatitis: This condition can present with hypopigmented patches, especially on the chest and back, but it typically involves more oily areas of the body and is associated with more inflammation.
- Vitiligo: Although vitiligo can cause hypopigmented patches, it typically does not present with fine scaling, and the patches are usually more sharply demarcated.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Leprosy (Hansen's Disease): Although rare, leprosy can cause hypopigmented skin lesions. It is crucial to consider this diagnosis, especially if the patient has been exposed to someone with leprosy or has recently traveled to an endemic area.
- Tuberculosis: Cutaneous tuberculosis can manifest as hypopigmented lesions, among other skin manifestations. A thorough history and additional testing would be necessary to consider this diagnosis.
- Rare diagnoses
- Idiopathic Guttate Hypomelanosis: This condition is characterized by small, discrete, hypopigmented macules, often on the arms and legs, but can appear on the trunk. It is more common in older adults but can occur in younger individuals.
- Progressive Macular Hypomelanosis: A rare condition that presents with hypopigmented macules, often on the trunk, which can coalesce into larger patches. It is more common in young adults and can be associated with fine scaling.