Monday, 30 December 2019

Pleural effusion and rheumatoid arthritis: Diagnostic value of the microscopic examination of pleural fluid

Written by Laura Sánchez Torres | Rafael Zambrana Moral | María Monsalud Arrebola Ramírez

Figure 1.  Cholesterol crystals in pleural fluid in light field at 400 increases to 1/10 dilution.

The image belongs to the pleural fluid (PF) of a 67-year-old man with a history of erosive rheumatoid arthritis (RA), who presented to the emergency department with progressive dyspnea. The chest radiograph performed at admission showed bilateral pleural effusion (PE), so he is admitted for complete his differential study between de novo heart failure or secondary to RA. The patient underwent four days of depletion treatment, after which control radiography showed complete resolution of the right PE and persistence of the left PE. This led to the performance of diagnostic thoracoscopy and evacuation of the persistent PE.
The PF sample received in the laboratory was milky in appearance with a Red blood cell count of 150/μL, a Total white blood cell count of 600/μL, with 85% polymorphonuclear leukocytes, and 15% mononuclear cells. The biochemical analysis was as follows: pH 7.285, Cholesterol 165 mg/dL, Triglycerides 16 mg/dL, Glucose 64 mg/dL, Total Proteins 5.25 g/dL, Lactate dehydrogenase (LDH) 1056 U/L, Adenosine deaminase (ADA) 45 U/L. In addition, in the observation under an optical microscope the presence of cholesterol crystals is detected (figure 1). These crystals are characterized by their various forms of presentation; such as rectangles, rods, needles, etc. They are colorless, transparent and irregular. The most characteristic crystals are those that appear as large rectangular plates (up to 100 μm in length) with a notch in one or more corners (figure 1).

Cholesterol crystals appear in pseudochylothrax, a rare form of PE that is characterized by its high cholesterol content. Macroscopically, its appearance is turbid or milky and its lack of clearing after centrifugation makes it possible to differentiate it from empyema. Its characteristics are: elevated cholesterol content (>200 mg/dL), low triglyceride levels (<50 mg/dL) although sometimes they can be high (50-110 mg/dL), and absence of chylomicrons. The presence of cholesterol crystals has diagnostic value, although it is not present in all cases of pseudoquilothorax. Pseudochylothrax is caused mainly by tuberculosis and to a lesser extent by RA. In the latter case only 3 - 5% of patients develop it at some point in their evolution (Canalejo Castrillero, 2005). It is usually unilateral, commonly occurring on the left side, is more frequent in males and is associated with the presence of rheumatoid nodules.

The right PE resolved after treatment and with the aid of the laboratory analysis, the patient was diagnosed with Contarini’s Syndrome. This syndrome refers to the occurrence of bilateral pleural fluid accumulation which can be explained by a different cause for each side, in this case one caused by an IC and another consequence of the RA presented by the patient.

 Therefore, it is important to highlight the importance of the laboratory in the microscopic examination of PE, where the biochemical parameters are fundamental for the differentiation between transudates and exudates, and the microscopic observation (figure 1) indispensable so that these findings do not go unnoticed, supporting the correct diagnosis of the patient and giving added value to the laboratory report.

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