What are the key diagnostic criteria and treatment regimens for classifying and managing Borderline Lepromatous (BL) vs Lepromatous Leprosy (LL) in a patient with suspected leprosy?

Classifying Borderline Lepromatous (BL) vs Lepromatous Leprosy (LL)

Classify BL versus LL leprosy primarily by the number and distribution of skin lesions, bacterial load on slit-skin smear, and histopathological architecture—BL presents with multiple but asymmetric lesions and moderately disorganized granulomas, while LL shows numerous symmetric lesions with massive foamy macrophage infiltration and higher bacillary counts. 1, 2, 3

Key Diagnostic Criteria

Clinical Features

Number and Distribution of Lesions:

• LL: Numerous erythematous papules, nodules, or infiltrative plaques with bilateral and symmetric distribution affecting face, hands, and feet; progresses to diffuse skin thickening and facial infiltration 1, 2
• BL: Multiple lesions but with less symmetry than LL; may present as localized disease in rare cases (though still multibacillary) 3, 4

Sensory Loss Pattern:

• Both BL and LL show less pronounced sensory loss compared to tuberculoid forms, but BL may show more variable nerve involvement 1, 2

Peripheral Nerve Thickening:

• Present in both forms but typically more symmetric and extensive in LL 2

Laboratory Diagnosis

Slit-Skin Smear (Bacillary Index):

• LL: Very high bacterial load (typically 4+ to 6+) with abundant acid-fast bacilli; morphologic index may be elevated in untreated cases 5, 4
• BL: Moderately high bacterial load but generally lower than LL 5, 6
• Obtain smears from multiple sites including earlobes, active lesion edges, and elbows 1, 2

Histopathological Examination (Gold Standard):

• LL: Atrophic epidermis with clear grenz zone (subepidermal clear zone); dermis shows massive infiltration of foamy macrophages densely packed with acid-fast bacilli; granulomas are absent or completely disorganized 1, 3, 4
• BL: Disorganized granulomatous structures (not completely absent); foamy macrophages present but with some attempt at organization; multiple acid-fast bacilli present but less dense than LL 3, 6
• Always obtain full-thickness skin biopsy from an active lesion edge, not the center 1, 5

Diagnostic Algorithm

1. Perform slit-skin smear from multiple sites (earlobes, active lesion edges, elbows) to determine bacterial load—bacillary index ≥4+ with symmetric distribution suggests LL 5, 4

2. Obtain full-thickness skin biopsy from active lesion edge and examine for:

   • Presence/absence of grenz zone (present in LL) 4
   • Degree of granuloma organization (completely disorganized/absent in LL; partially organized in BL) 3, 6
   • Density of foamy macrophages and bacillary load 3, 4

3. Assess clinical distribution pattern:

   • Bilateral symmetric involvement of face, hands, feet = LL 1, 2
   • Multiple but less symmetric lesions = BL 3

Critical Pitfalls to Avoid

Do not rely on clinical examination alone—histopathological examination is essential for accurate classification, as clinical-histopathological concordance is only 60% with maximum disparity (52.9%) in the borderline spectrum 5

Do not undertake localized presentations of multibacillary disease—rare cases of LL can present with only 1-2 lesions but still show high bacillary loads on smear and typical LL histopathology; these require full multibacillary treatment 4

Obtain biopsy even from normal-appearing skin in suspected cases—52% of normal-appearing skin in leprosy patients shows classic histopathological features, which can aid in classification 6

Treatment Classification

Both BL and LL are classified as multibacillary (MB) disease and require the same WHO multidrug therapy regimen: rifampin, clofazimine, and dapsone for 12 months 1, 2, 5

Screen for G6PD deficiency before initiating dapsone to prevent hemolytic anemia 1

Obtain baseline ECG before clofazimine due to QT prolongation risk 1