Laboratory Assessment of Patients with Systemic Mastocytosis

肥大细胞增多症可能有不同的临床表现，这取决于肥大细胞负荷和组织受累的程度。儿童主要是良性疾病，疾病仅限于皮肤，诊断为三种皮肤变异之一：斑丘性皮肤肥大细胞增多症(MPCM)、弥漫性皮肤肥大细胞增生症(DCM)或肥大细胞瘤(MTOMA)。全身性肥大细胞增多症通常见于KIT中有体细胞突变的成年人。然而，儿童也可能有全身性疾病，KIT在婴儿时期就有类似的突变。利用等位基因特异性定量聚合酶链式反应检测成人肥大细胞增多症患者外周血中的KIT D816V，已被报道在肥大细胞增多症的诊断、疾病负担评估和治疗中具有价值。为了检验这项检测在有皮肤肥大细胞增多症表现的儿童中的价值，我们评估了65名患有儿科发作性肥大细胞增多症所有变种的患者的数据，包括那些已知的系统性疾病，以将KIT突变状态与临床表现、血清类胰蛋白酶水平和骨髓组织病理学联系起来。 仅在皮肤病患者(MCPM、DCM和MTOMA，n=37)以及无器质性肿大史的儿科患者中，KIT D816V突变的PB ASqPCR始终为阴性。在23例诊断为系统性疾病的患者中，PBASqPCR阳性16例(0047384%)。2例伴有Kit D816Y相关系统性疾病(血清类胰蛋白酶184和244 ng/ml)的ISM患者、1例骨髓诊断为ISM且骨髓标本中未检测到KIT突变的患者，以及4例经骨髓活检诊断为ISM的患者，PB ASqPCR均为阴性。后4例患者的骨髓活检组织中肥大细胞疾病负担较低(肥大细胞占骨髓细胞总数的5%)，但其骨髓标本经RT-PCR/RFLP检测为KIT D816V突变阳性。由于这4例患者在最初的骨髓活检过程中没有进行Kit D816V突变的外周血聚合酶链式反应，所以我们获得了在骨髓活检过程中收集的冰冻外周血样本，并用ASqPCR对其进行了检测。四个样本的结果都是阴性的。此外，他们的临床状况有了显著的改善，主要或完全消除了皮肤损伤，血清类胰蛋白酶显著下降(平均为339至110 ng/ml)，在713年的时间里，药物使用量从每天服用减少到需要的药物。PB ASqPCR试剂盒D816V对各种皮肤病的特异性均为100%。当骨髓活检证实时，检测全身性疾病的敏感度为696%。我们对大多数患者(615%)进行了外周血单核苷酸定量聚合酶链式反应检测。当随访36个月时，数据发现产生了一致的结果。阳性的患者仍然是阳性的，这些结果继续与血清类胰蛋白酶的值相关。此外，负值患者仍为负值。 这些发现是开发一种算法的基础，该算法有助于决定何时对出现肥大细胞增多症皮肤症状的儿童进行骨髓活检。

Mastocytosis may present with varied clinical manifestations depending on the mast cell burden and the extent of tissue involvement. Children are primarily represented on the benign end of the disease spectrum, with disease limited to skin and diagnosed with one of three cutaneous variants; maculopapular cutaneous mastocytosis (MPCM), diffuse cutaneous mastocytosis (DCM) or mastocytoma (MTOMA). Systemic mastocytosis is typically seen in adults with somatic mutations in KIT. However, children may also have systemic disease, with similar mutations in KIT and as early as infancy.The use of allelespecific quantitative polymerase chain reaction to identify KIT D816V in the peripheral blood of adults with mastocytosis has been reported to have value in the diagnosis, assessment of disease burden and management of this disease. To examine the value of this assay in children with cutaneous manifestations of mastocytosis, we assessed data on 65 patients with all variants of paediatriconset mastocytosis, including those known to have systemic disease, to correlate KIT mutation status with clinical findings, serum tryptase levels and bone marrow histopathology. The PB ASqPCR for the KIT D816V mutation was consistently negative in patients with cutaneous disease only (MCPM, DCM and MTOMA, n = 37) and without a history of organomegaly documented to be associated with systemic disease in paediatric patients. Of the 23 patients diagnosed with systemic disease (ISM), the PB ASqPCR was positive in 16/23 samples (0047384%). PB ASqPCR was negative in two ISM patients with organomegaly that had KIT D816Yassociated systemic disease (serum tryptase values 184 and 244 ng/ml), one patient with a bone marrow diagnosis of ISM and no KIT mutations detected in the marrow samples, as well as four patients diagnosed with ISM by bone marrow biopsy. These latter four patients had a low mast cell disease burden in bone marrow biopsies (mast cells 5% of total marrow cells); but positive KIT D816V mutation by RTPCR/RFLP in their marrow samples. As PB ASqPCR for the KIT D816V mutation was not performed at the time of the original bone marrow biopsy procedure in these four patients, we obtained their frozen PB samples collected at the time of the bone marrow biopsy procedure and analyzed them using ASqPCR for the KIT D816V mutation. The results were negative in all four samples. In addition, there has been a significant improvement in their clinical status, as evidenced by a major or complete resolution of skin lesions, a significant decrease in serum tryptase (average 339 to 110 ng/ml) and a decrease in medication usage to as needed medications from daily dosing over a period of 713 years. The specificity of PB ASqPCR KIT D816V assay was 100% for all variants of cutaneous disease. The sensitivity for the detection of the systemic disease when documented with a marrow biopsy, was 696%. We performed followup PB ASqPCR testing in most patients (615%). Data was found to yield consistent results when followed up to 36 months. Patients with a positive value remained positive and these results continued to correlate with serum tryptase values. In addition, the patients with negative values remained negative. These findings were the basis of the development of an algorithm to assist in the decision for when to perform a bone marrow biopsy in children presenting with cutaneous manifestations of mastocytosis.