Accuracy of the Polymerase Chain Reaction of Ulnar Perineural Subcutaneous Aspirate Guided by Ultrasound for the Diagnosis and Monitoring of Leprosy Cure

Leprosy is a chronic infectious disease caused by Mycobacterium leprae and is characterized by skin and peripheral nerve involvement. Neural impairment is the main determinant of disability and long-term morbidity. Early diagnosis remains challenging because current diagnostic methods have important limitations. Slit-skin smear microscopy and skin biopsy have low sensitivity in many clinical settings, especially in paucibacillary and primary neural forms. Nerve palpation is widely used but lacks reproducibility and does not distinguish among etiologies of neuropathy. Nerve biopsy, although more precise in selected cases, is invasive and may cause permanent neurological sequelae.

High-resolution ultrasonography has emerged as a promising tool for evaluation of leprosy neuropathy because it allows objective assessment of peripheral nerve cross-sectional area, asymmetry, fascicular abnormalities, and intraneural or epineural hypervascularity using Doppler. However, ultrasound cannot directly detect the bacillus.

Molecular methods have expanded the diagnostic possibilities in leprosy. Real-time PCR targeting the repetitive element RLEP can detect M. leprae DNA with high sensitivity. However, DNA detection alone does not distinguish viable from non-viable bacilli. Detection of RNA by RT-PCR, including targets such as 16S rRNA and sodA, may provide evidence of bacillary viability because RNA degrades rapidly after cell death. This approach may improve treatment monitoring and refine the concept of cure.

The present study proposes a minimally invasive strategy based on ultrasound-guided ulnar perineural subcutaneous aspirate. Biological material will be collected adjacent to the affected nerve, avoiding direct nerve biopsy and potentially increasing the sensitivity of molecular detection in the neural microenvironment. Participants with suspected leprosy will be assessed clinically, by high-resolution ultrasound of the ulnar nerves, and by molecular detection of M. leprae DNA and RNA in aspirated material. They will be evaluated at baseline, near the time of diagnosis, and after one year of treatment.

The main objective is to determine the diagnostic accuracy of ultrasound-guided perineural aspirate PCR/RT-PCR compared with conventional methods. Secondary objectives include correlation of ultrasound abnormalities with molecular positivity, assessment of bacillary viability over time, and development of workflows potentially applicable to the public health system, including referral centers and settings using portable ultrasound.