For a patient suspected of having leprosy, should histopathology be performed or is a slit skin smear (SSS) sufficient to initiate multidrug therapy (MDT) according to Indian guidelines?

Leprosy Diagnosis: Clinical Classification Alone is Sufficient to Initiate MDT

According to Indian practice patterns and WHO guidelines, slit-skin smear (SSS) is NOT necessary to start multidrug therapy (MDT) for leprosy—clinical classification based on the number of skin lesions and nerve involvement is sufficient to initiate treatment. 1

Clinical Classification is the Primary Basis for Treatment

• Leprosy classification for treatment purposes relies on counting skin lesions and assessing nerve involvement, not on bacteriological confirmation. Patients with 1-5 lesions are classified as paucibacillary (PB) and receive 6 months of MDT, while those with >5 lesions are classified as multibacillary (MB) and receive 12 months of MDT. 2

• The diagnosis of leprosy should be made from the clinical picture, complemented by skin bacilloscopy and histopathology when available, but treatment should not be delayed waiting for these confirmatory tests. 2

The Limited Role of Slit-Skin Smear

• SSS is routinely performed in many Indian centers but adds minimal value for classification purposes. In a study from Ethiopia examining 183 newly diagnosed leprosy patients, SSS was performed on 150 clinical MB patients and all 17 clinical PB patients—yet not a single patient with clinical PB classification was reclassified to MB based on SSS results. 1

• SSS has poor sensitivity in paucibacillary disease (only 1.8% positive in PB cases), making it essentially useless for this group. Even in MB cases, SSS sensitivity is only 59.8%, meaning it misses a substantial proportion of cases. 3

• The study concluded that SSS microscopy was performed routinely without changing the classification and management of patients, representing a waste of time and resources. 1

When Histopathology Should Be Considered

While histopathology is not required to initiate MDT, it has specific valuable roles:

• Histopathology is most useful in diagnostically challenging cases where clinical features are atypical or uncertain. The diagnosis should be complemented by histopathology when the clinical picture is unclear. 2

• Histopathology provides prognostic information post-treatment. The presence of foamy granuloma (OR=7.36) and histological bacillary index ≥1+ (OR=1.55) are significantly associated with treatment failure, making biopsy valuable for monitoring high-risk patients after MDT completion. 4

• Histopathology helps differentiate leprosy types along the spectrum (TT, BT, BB, BL, LL). Correlation between clinical, histopathological, and bacteriological findings improves diagnostic accuracy, with 80% correlation between clinical and histopathological examinations in one study. 5

Practical Algorithm for Initiating MDT

1. Count skin lesions and assess for nerve involvement clinically
2. Classify as PB (1-5 lesions) or MB (>5 lesions) 1
3. Initiate appropriate MDT regimen immediately (PB: 6 months; MB: 12 months) 2
4. Reserve SSS and histopathology for:
   • Diagnostically uncertain cases 2
   • Post-treatment monitoring for relapse risk 4
   • Research or academic purposes 1

Common Pitfalls to Avoid

• Do not delay treatment waiting for SSS or histopathology results. Early diagnosis and therapy is the most important strategy for leprosy control. 2

• Do not rely on SSS to "rule out" MB disease in clinically PB cases. SSS has extremely poor sensitivity (1.8%) in PB leprosy and will not change management. 3

• Do not perform routine SSS on all leprosy patients. This represents an inefficient use of resources without clinical benefit, as demonstrated in the Ethiopian study where routine SSS changed management in zero patients. 1