What are the differential diagnoses for an exudative pleural effusion?

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滲出性胸水の鑑別疾患

滲出性胸水の主要な鑑別疾患は、悪性腫瘍、肺炎/膿胸、結核、肺塞栓症、膠原病（特に関節リウマチ）、食道破裂、膵疾患であり、これらで滲出性胸水の大部分を占める。1

主要な鑑別疾患

最も頻度の高い疾患

  • 悪性腫瘍：滲出性胸水の最も一般的な原因の一つ1, 2

    • 肺癌が最多、次いで乳癌3
    • 細胞診での診断率は約60%のみ1
    • 血性胸水の場合、悪性腫瘍の可能性が高い1

  • 肺炎/膿胸：感染性胸水1, 4

    • pH < 7.2は感染を強く示唆1
    • 嫌気性菌感染では特徴的な悪臭1
    • 最も低いグルコース値を示す（関節リウマチと並んで）1

  • 結核性胸膜炎：1, 4

    • グルコース < 3.3 mmol/Lを示すことが多い1
    • 胸腔鏡検査でほぼ100%診断可能5

  • 肺塞栓症：1

    • 約75%で胸膜痛を伴う1
    • 呼吸困難が胸水の量に比して強い1
    • 胸水検査では診断困難なため、高い臨床的疑いが必要1

pH・グルコースによる鑑別

pH < 7.2（正常血液pHの場合）を示す6つの疾患：1, 6

  1. 膿胸
  2. 悪性腫瘍
  3. 膠原病（特に関節リウマチ）
  4. 結核
  5. 食道破裂
  6. 血胸

グルコース < 3.3 mmol/Lを示す疾患：1

  • 膿胸
  • 関節リウマチ（最も低値）
  • ループス
  • 結核
  • 悪性腫瘍
  • 食道破裂

アミラーゼ上昇を伴う疾患

胸水/血清アミラーゼ比 > 1.0または胸水アミラーゼが血清正常上限を超える場合：1

  • 急性膵炎
  • 膵仮性嚢胞
  • 食道破裂（唾液型アミラーゼ）
  • 悪性腫瘍（約10%で上昇）1

血性胸水の原因

著明な血性胸水（ヘマトクリット > 末梢血の50%）：1

  • 悪性腫瘍
  • 肺塞栓症（梗塞を伴う）
  • 外傷
  • 良性石綿胸水
  • 心損傷後症候群

診断アプローチの重要ポイント

胸水性状の観察1

  • 混濁・乳白色：遠心分離後
    • 上清が透明 → 膿胸（細胞成分）
    • 上清も混濁 → 乳び胸・偽乳び胸（脂質成分）

細胞分画3

  • リンパ球優位：悪性腫瘍、結核を示唆
  • 好酸球 > 25%：悪性腫瘍を除外しない3

予後予測因子

悪性胸水でpH < 7.3の場合：1

  • pH > 7.3：生存期間中央値 9.8ヶ月
  • pH < 7.3：生存期間中央値 2.1ヶ月

臨床的注意点

見逃してはいけない疾患

  1. 食道破裂：唾液型アミラーゼ上昇、pH < 7.21
  2. 膿胸への進展：肺炎随伴胸水で必ず評価2
  3. 薬剤性胸水：チロシンキナーゼ阻害薬が現在最多7

診断精度向上のために

  • 微生物検査：血液培養ボトルと滅菌容器の両方に提出（診断率向上）1
  • 細胞診：初回陰性でも2回目実施を推奨1
  • 造影CT：胸水貯留状態で施行（胸膜の評価に最適）1
  • 胸腔鏡検査：診断率約95%、悪性腫瘍97%、結核ほぼ100%5

References

2
Research

Pleural Effusion in Adults-Etiology, Diagnosis, and Treatment.

Deutsches Arzteblatt international, 2019

3
Guideline

management of malignant pleural effusions.

American Journal of Respiratory and Critical Care Medicine, 2000

4
Research

Diagnostic approach to pleural effusion in adults.

American family physician, 2006

5
Research

[Current diagnostic approach to pleural effusion].

Pneumologie (Stuttgart, Germany), 2004

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