Leprosy in the United States: Epidemiology, Clinical Features, and Diagnosis

Conclusions

• Leprosy remains clinically relevant in the United States despite being considered eliminated globally, because new cases continue to occur and some arise without classic travel or exposure risks.
• Most people are naturally resistant to leprosy, so transmission usually requires prolonged close contact rather than casual day-to-day exposure.
• The U.S. epidemiology is changing, with evidence of autochthonous domestic transmission and possible zoonotic spread linked to armadillos, whose habitat is expanding northward.
• Stigma is a major barrier to detecting and reporting leprosy, likely causing underestimation of the true global burden.
• Mycobacterium lepromatosis is an additional leprosy-causing species, can present with diffuse lepromatous disease, and should be considered even in patients without obvious travel history.
• Because the organism cannot be cultured easily, diagnosis depends on maintaining clinical suspicion, recognizing sensory loss and nerve enlargement, and using biopsy, slit-skin smear, and PCR when available.
• Classification systems are clinically useful because they distinguish unstable forms prone to reactions and help guide treatment decisions.
• Leprosy exists on an immunologic spectrum from tuberculoid to lepromatous disease, with increasing bacillary burden and worsening cell-mediated immunity as disease becomes more lepromatous.
• Early sensory loss, especially loss of temperature sensation, along with anhidrotic patches and hair loss are important clues to early or paucibacillary disease.
• Advanced lepromatous disease can involve the face, upper airway, testes, eyes, and peripheral nerves, showing that leprosy is a multisystem disease, not just a skin disorder.
• Nerve injury is the main driver of long-term disability, so early recognition, biopsy, and treatment are critical to preventing morbidity.
• Even in non-endemic settings, dermatologists should keep leprosy in the differential for anesthetic, dry, hypopigmented or erythematous plaques with nerve enlargement.