The accuracy of the Montenegro skin test for leishmaniasis in PCR-negative patients

Abstract INTRODUCTION: As highly specific molecular biology-based techniques may not be sensitive enough for the diagnosis of American tegumentary leishmaniasis (ATL), clinicians frequently rely on immunological tests before treatment initiation. Hence, the correct combination of diagnostic tests is imperative for ATL diagnosis. We aimed to evaluate the accuracy of the Montenegro (Leishmanin) skin test (MST) in polymerase chain reaction (PCR)-negative patients to accurately detect ATL. METHODS: Patients with a clinical picture compatible with ATL were divided into ATL (confirmed by lesion smear, culture indirect immunofluorescence, and/or histopathology) and no-ATL (diseases that can mimic leishmaniasis) groups. Conventional PCR for the minicircle kDNA of Leishmania was performed, and the MST was carried out for PCR-negative patients. RESULTS: Ninety-nine patients were included in this study, including 79 diagnosed with ATL (6 with mucocutaneous leishmaniasis) and 20 without ATL (no-ATL group). The MST showed a high sensitivity of 90.0% (95% confidence interval [CI] = 69.90-97.21) in PCR-negative patients that was 10% higher than the sensitivity reported in PCR-positive population (79.66%; 95% CI = 67.73-87.96). CONCLUSIONS: One of the most important reasons for PCR negativity among patients with active ATL is the presence of a strong cellular immunological response, especially in chronic and mucocutaneous leishmaniasis. This reinforces the considerable utility of the tests that detect cellular responses against Leishmania antigens such as the MST in PCR-negative patients when the performance in screening situations is questionable.

**摘要**：
**引言**：鉴于基于分子生物学的高特异性技术对美洲皮肤利什曼病（American tegumentary leishmaniasis, ATL）的诊断敏感性不足，临床医师常在治疗启动前依赖免疫学检测手段。因此，合理组合诊断检测方案对ATL的诊断至关重要。本研究旨在评估蒙氏（利什曼素）皮肤试验（Montenegro (Leishmanin) skin test, MST）在聚合酶链反应（polymerase chain reaction, PCR）检测阴性患者中的诊断准确性，以精准检出ATL。

**方法**：将临床表现符合ATL的患者分为ATL组（经皮损涂片、培养、间接免疫荧光法及/或组织病理学确诊）与非ATL组（需与利什曼病鉴别的其他疾病）。对所有受试者开展利什曼原虫动基体小环DNA常规PCR检测，并对PCR检测阴性的患者实施MST检测。

**结果**：本研究共纳入99例患者，其中79例确诊为ATL（含6例皮肤黏膜利什曼病），20例为非ATL患者。在PCR检测阴性的患者中，MST的灵敏度高达90.0%（95%置信区间[CI]：69.90~97.21），较PCR检测阳性人群的报道灵敏度（79.66%；95%CI：67.73~87.96）高出10个百分点。

**结论**：活动性ATL患者出现PCR检测阴性的最重要原因之一，是机体存在强烈的细胞免疫应答，尤以慢性感染及皮肤黏膜利什曼病患者为甚。这一结果进一步证实，当筛查场景下的检测性能存疑时，针对利什曼原虫抗原的细胞免疫应答检测（如MST）在PCR阴性患者中具备较高的应用价值。