高齢者肺結核患者に対する高分解能CT検査の放射線学的意義-培養検査を用いた解析-．

Radiological significance of high-resolution computed tomography for elderly pulmonary tuberculosis patients - an analysis with culture test.

• Niranjan Sahu
• Somadatta Das
• Rabindra Nath Padhy

抄録

目的:

肺結核（PTB）は高齢者の主要な健康問題の一つであり，重大な罹患率と死亡率の原因となっている．本研究の目的は，肺結核（PTB）の診断における高分解能コンピュータ断層撮影法（HRCT）の意義を，培養検査と比較して評価することである．

Purpose: Pulmonary tuberculosis (PTB) is one of the major health problems in the elderly population, causing significant morbidity and mortality. The aim of this study is to evaluate the significance of the high-resolution computed tomography (HRCT) modality for the diagnosis of PTB, in comparison to culture test.

材料と方法:

臨床的にPTBが疑われ、塗抹と培養の報告を受けた124人の患者からなる研究集団の胸部HRCT画像を用いて、HRCT検査の感度と特異度を分析した。活動性PTBの特徴は、遠心結節、「ツリーインバッド」パターンの密度、マクロ結節、コンソリデーション、空洞性病変、グランドガラスの不透明性、および粟粒結節であった。

Material and methods: Thoracic HRCT images of the study population, comprising 124 patients clinically suspected for PTB with smear and culture reports, were analysed for sensitivity and specificity of the HRCT test. Features of active PTB were centrilobular nodules, 'tree-in-bud' pattern densities, macro-nodules, consolidations, cavitary lesions, ground-glass opacities, and miliary nodules.

結果:

調査集団のうち、108例は活動性PTBのHRCT特徴を呈し、残りの症例は陰性であったが、PTBを模倣した特徴をいくつか呈していた。培養検査が陽性であった106例は活動性PTBであり、残りの症例は培養陰性であった。誤陽性（FP）またはI型エラー、偽陰性（FN）またはII型エラーをベイズの定理で判定した。HRCT検査の感度（真陽性率）は0.8125、特異度（真陰性率）は0.8571であった。

Results: Among the study population, 108 cases presented HRCT features of active PTB and the remaining cases were negative but had presented a few features mimicking PTB. As inferred from positive culture test results, 106 cases had active PTB, the remaining cases were culture negative for PTB. False-positive (FP) or 'type I error' cases, and false-negative (FN) or 'type II error' cases were ascertained by Bayes' theorem. Sensitivity (true positive rate) and specificity (true negative rate) of HRCT test were 0.8125 and 0.8571, respectively.

結論:

適切な診断のための予測能力を2つの「事後確率」の値で計算したところ，HRCTの「事後確率」の平均値は0.6358であった．培養検査が陽性の場合、HRCT検査の陽性判定率は69.56～92.85％であり、一方、培養検査が陰性の場合、陰性判定率は66.66～100％であった。このように、HRCT検査はかなり信頼性の高い検査である。

Conclusions: For proper diagnosis the predictive capability, as two values of 'a posteriori probability', was computed; the mean value of 'a posteriori probability' for HRCT was 0.6358. When its culture test was positive, the HRCT test was 69.56-92.85% efficient in ascertaining positive results with a sample; on the other hand, when its culture test was negative it was 66.66-100% efficient for a negative result. Thus, the HRCT test is considerably dependable.

Copyright © Polish Medical Society of Radiology 2020.