Differential Diagnosis for the Outbreak

The clinical presentation of dry lesions on the forearms and lower extremities, small nonulcerated dry plaques, a large encrusted ulcer with a well-demarcated appearance, and regional lymphadenopathy in military personnel returning from the Middle East suggests several potential diagnoses. Here is the differential diagnosis organized into categories:

• Single Most Likely Diagnosis

  • Cutaneous Leishmaniasis: This is the most likely diagnosis given the clinical presentation and the epidemiological context. Cutaneous leishmaniasis is common in the Middle East and is characterized by skin lesions that can range from small, nonulcerated plaques to large, ulcerated lesions with a well-demarcated edge. The disease is transmitted by the bite of an infected sand fly, which is prevalent in the region.

• Other Likely Diagnoses

  • Brucellosis: While brucellosis can present with a wide range of symptoms, including skin manifestations, it is less likely to cause the specific type of skin lesions described. However, given the exposure history and the fact that brucellosis can be contracted through contact with infected animals or their products, it remains a consideration.
  • Lyme Disease: Lyme disease, caused by Borrelia burgdorferi and transmitted by tick bites, can present with a variety of skin manifestations, including the characteristic "bull's-eye" rash (erythema migrans). However, the lesions described in the scenario do not closely match the typical presentation of Lyme disease, making it less likely.

• Do Not Miss Diagnoses

  • Squamous Cell Carcinoma: Although the clinical presentation does not strongly suggest squamous cell carcinoma, any skin lesion that does not heal or changes in appearance should be biopsied to rule out malignancy. Given the potential for serious consequences if missed, it is crucial to consider and rule out cancer.
  • Toxoplasmosis: Toxoplasmosis is less likely to cause the specific skin lesions described but can have a wide range of presentations, especially in immunocompromised individuals. It is essential to consider toxoplasmosis due to its potential severity, especially if the patients are immunocompromised or if there are other systemic symptoms.

• Rare Diagnoses

  • Other rare infectious diseases that could potentially cause similar skin lesions, such as Leptospirosis or Rickettsial infections, should be considered based on the exposure history and travel to endemic areas. However, these would be less likely given the specific clinical presentation and the context provided.