# Presumed Very Late Relapse of Lepromatous Leprosy 35 Years After Treatment: A Diagnostic Challenge in a Non-endemic Setting

## TL;DR

A rare case of leprosy relapse 35 years after treatment is reported in a non-endemic country, highlighting diagnostic challenges and the need for long-term monitoring.

## Contribution

This case presents a presumed very late relapse of lepromatous leprosy in a non-endemic setting, emphasizing diagnostic difficulties and long-term vigilance.

## Key findings

- M. leprae was molecularly detected in a skin biopsy despite no histopathological signs of active disease.
- The case suggests a very late relapse due to the long disease-free interval and lack of reinfection risk factors.
- The case underscores the importance of clinical awareness of leprosy in non-endemic regions.

## Abstract

Leprosy is a chronic infectious disease caused by Mycobacterium leprae that primarily affects the skin and peripheral nerves. Although eliminated as a public health problem in many countries, it remains an important neglected tropical disease, with more than 174,000 new cases reported worldwide in 2023, predominantly in endemic regions such as India, Brazil, and Indonesia. We report a rare case of a presumed very late relapse of lepromatous leprosy occurring 35 years after treatment completion in a patient from a non-endemic European setting. The patient presented with progressive sensorimotor neuropathy, progressive deformities, and a chronic non-healing plantar ulcer. Historical records confirmed biopsy-proven lepromatous leprosy at the initial diagnosis, with documented cure following multidrug therapy. Current evaluation revealed the molecular detection of M. leprae in a skin biopsy, although histopathological features of active disease were not demonstrated. Given the absence of epidemiological risk factors for reinfection, the long disease-free interval, and the overall clinical and microbiological context, a very late relapse was considered the most plausible explanation. This case highlights the diagnostic challenges of leprosy in non-endemic settings and underscores the importance of long-term clinical vigilance and awareness of late complications.