Chocolate-Colored Pseudochylothorax in a Woman with a History of Pleuropulmonary Tuberculosis

Background

Pseudochylothorax, also known as cholesterol effusion or chyliform effusion, is one of two types of lipid pleural effusions. This group of effusions, composed of chylothorax and pseudo-chylothorax, is usually unilateral [1,2] and can be recognized by the high lipid content and characteristic cloudy or milky appearance [3,4]. Although similar, chylothorax and pseudochylothorax represent distinct entities with different etiologies, clinical implications, and treatments [5–9]. Chylothorax was first described by Bartolet in 1633 as the accumulation of chyle in the pleural space and is usually associated with rupture or obstruction of the thoracic duct [10]. It is characterized by a lipid-rich fluid with a high content of triglycerides (>110 mg/dL), the presence of chylomicrons, and the absence of cholesterol crystals [1,2,9]. Pseudochylothorax was first described by Bruce F. Weems in 1918 as the accumulation of a cholesterol crystal-rich fluid within the pleural space [11]. Although pseudochylothorax is also composed of a lipid-rich fluid, it has a high cholesterol content (>200 mg/dL) and a lower triglyceride concentration (<110 mg/dL). It often has cholesterol crystals on microscopy, which cannot be attributed to thoracic duct involvement [4,12].

Analysis of pleural fluid with the measurement of cholesterol and triglyceride levels is of paramount importance for the distinction between the two types of lipid effusions [7]. Confirmation of the effusion type is assessed mainly by the absence of chylomicrons in the pseudochylothorax fluid [13]. Because pseudochylothorax is a rare entity, epidemiological studies of pseudochylothorax are limited, but there have been a few hundred case reports worldwide [5].

The main clinical conditions that predispose patients to the development of pseudochylothorax are tuberculosis and rheumatoid arthritis. Rarer causes include empyema with incomplete treatment, hemothorax, pleuropulmonary paragonimiasis, alcoholism, syphilis, and hepatopulmonary echinococcosis [7]. Additionally, rare malignant causes of pseudochylothorax exist, including lung cancer and, more recently reported, pleural mesothelioma [14]. Other reported causes are yellow nail syndrome, iatrogenesis, and Demos-Meigs syndrome [5]. Rheumatoid-associated pseudochylothorax can have a relatively rapid onset, with a median duration of symptoms of 15 months, and does not show typical pleural thickening [15,16]. Clinically, patients with pseudochylothorax can be asymptomatic in up to one-third of cases [17] or can present symptoms of dyspnea and chest pain [5]. Symptoms can be associated with the underlying disease or with the inflammatory and restrictive process of the pleura itself. The pleura is often thickened and can present calcifications [5]. The diagnosis of chyliform effusion is based on the analysis of the aspirated fluid in thoracentesis and should be considered a diagnostic hypothesis in cases of chronic pleural effusions associated with fibrosis and pleural thickening [7].

Case Report

The patient was a 55-year-old woman with a history of pulmonary tuberculosis treated at the age of 10 years without complications with a combination of isoniazid, rifampicin, and pyrazinamide. She had a history of childhood asthma and plantar psoriasis, with regular topical use of clobetasol propionate for dermatologic disease to date. At 40 years of age, she presented with a new pulmonary infection due to tuberculosis, which was treated for 1 year, owing to the development of drug-related hepatitis related to the therapeutic regimen (combination of isoniazid, rifampicin, ethambutol, and pyrazinamide), requiring an alternative regimen (combination of streptomycin, ethambutol, and ofloxacin). During the second treatment, the patient experienced a sudden onset of pleuritic pain. A chest computed tomography (CT) was performed and showed the presence of pleural effusion on the left, but was not addressed at this time. Five days after CT, she again became asymptomatic and remained so until the end of the tuberculosis treatment. Thirteen years after completing the tuberculosis treatment, she developed general fatigue and dyspnea on exertion. Symptoms progressively worsened over 3 months. At that time, a chest X-ray revealed homogeneous hypotransparency in the lower half of the left hemithorax with effacement of the costophrenic sinus, suggesting pleural effusion. In light of this finding, a new CT of the chest was requested. Results of the chest CT confirmed the presence of pleural collection in the same site where the previous CT had shown pleural effusions 3 months prior, suggesting chronic evolution with encystation. In addition, thickening of the pleural leaflets with foci of calcification on the left was observed and associated with reduced volume of the ipsilateral lung (Figure 1).

The patient was then admitted and on day 1 of admission, she underwent diagnostic ultrasound-guided thoracentesis. The liquid collected was thick, chocolate-colored (Figure 2), with the following biochemical characteristics: pH, 7.3; glucose, 37.9 mg/dL; lactate dehydrogenase (LDL), 2059.8 IU/L; total protein, 8.8 mg/dL; triglycerides, 90 mg/dL; adenosine deaminase, 56 IU/L; and cholesterol, 300 mg/dL. These levels characterized the effusion as a pseudochylothorax. Cellularity showed 631 000 leukocytes/µL, with 87.9% polymorphonuclear cells. The culture for common organisms was negative. Assessment of acid-fast bacilli and the culture for Mycobacterium tuberculosis cultures were also negative. Similarly, the polymerase chain reaction (PCR) for M. tuberculosis (GeneXpert) and the direct search and culture for fungi were also negative. Cytology of the pleural fluid showed cell debris, some lymphocytes and rare red blood cells, which were negative for malignant cells.

Fecal sample and serum IgG serology for Entamoeba histolytica was negative. Due to logistical issues at our institution, pleural biopsy was unfortunately not performed.

It is noteworthy that during the second treatment of tuberculosis, the patient did not undergo thoracentesis or any treatment for pleural effusion, although she successfully completed the drug treatment with considerable clinical improvement. Owing to the patient’s respiratory symptoms persisting even after 3 days of hospitalization, evacuation thoracentesis was performed to promote improvement of respiratory symptoms. After the procedure, the patient showed improvement of symptoms and remained asymptomatic. She was discharged 5 days after admission. A point-of-care lung ultrasound performed 6 months after presentation showed no recurrence of the pleural effusion.

Discussion

Although pseudochylothorax has most commonly been described with a cloudy, milky appearance similar to chylous effusions, it is worth noting that it can appear opalescent in many cases, with a dark yellow color described as having a “machine oil appearance” [14,18]. Despite the chocolatey appearance of the liquid in this case report not being typical, a case series of chyliform effusions was published, in which 1 patient also presented a chocolate-colored effusion [17]. The patient in question was a man born in 1920 who was diagnosed and treated for pulmonary tuberculosis with pneumothorax and repeated courses of antibiotic therapy. He developed a chocolate-colored effusion with high cholesterol content that required relief thoracentesis due to effusion recurrence and respiratory symptoms [17].

The liquid collected from a patient with pseudochylothorax usually has a cholesterol concentration greater than 200 mg/dL, a triglyceride level less than 110 mg/dL, and a cholesterol/triglyceride ratio >1. It may or may not contain cholesterol crystals on microscopy [5,7,13]. The biochemical analysis often shows exudative fluid, with pH <7.2, glucose <60 mg/dL, protein concentration ranging between 4 and 7 g/dL, and high LDL. Neutrophils predominate among the cell types [13], showing a neutrophilic inflammatory process. In the present case, the characteristics of the fluid were compatible with pseudo-chylothorax. Although a pleural fluid cholesterol value greater than 200 mg/dL is strongly suggestive of pseudochylothorax, the evidence to support this diagnostic cutoff is limited [19]. In fact, approximately a quarter of cases of pseudochylothorax present a cholesterol value in the pleural fluid below 200 mg/dL and some cases can reach values as low as 120 mg/dL [5].

The pathophysiology of chyliform effusions is not yet fully understood, but the main hypothesis for the development of pleural effusion is based on inflammatory processes with chronification that evolve to visceral and parietal leaflet stiffening and fibrosis [17]. These changes hinder the physiological drainage of pleural fluid, favoring the accumulation of cell lysis products, especially neutrophils and erythrocytes. These neutrophils and erythrocytes have high levels of cholesterol and lecithin-globulin complexes in their cytoplasm, which would be the source of the high levels of lipids in the liquid [7]. Another possible explanation is that cholesterol is derived from serum lipoproteins, which would also be trapped in the pleural space and consequently be transferred to high-density lipoproteins due to the stiffening and fibrosis of the leaflets [7]. The patient reported here belongs to the group of patients with a chronic inflammatory process in the pleura. After the second time the patient was treated for tuberculosis, pleural effusion had already been observed, but this was not addressed. It is interesting to note that despite not approaching the liquid, it seems that it remained sterile, since the direct test cultures and PCR for M. tuberculosis were negative in the current analysis of the liquid.

The management of pseudochylothorax depends on the underlying disease with which it is associated and its appropriate treatment [7,13,20]. Management evolves favorably in most cases, without the need for intervention [18]. Patients who present symptoms due to the mechanical effects of pleural effusion, such as restriction or dyspnea [7] or a progressive increase in the amount of pleural fluid, can undergo relief thoracentesis. In cases of recurrence of the effusion and symptoms after drainage, decortication surgery [7,13,20] or pleurodesis [13] should be performed, with consideration to the knowledge that repeated drainage can generate complications such as empyema and pleurocutaneous fistulas. It is extremely important to treat and/or screen for rheumatoid arthritis and tuberculosis in patients diagnosed with pseudochylothorax since these are the 2 main etiologies of this type of pleural effusion [7]. The patient presented here was treated with evacuatory thoracentesis, which was followed by a good evolution. Notably, we chose this procedure because it is less invasive and does not require hospitalization. Another factor that contributed to this choice was the COVID-19 pandemic, as the patient was initially evaluated at a time when many hospital beds in Brazil were occupied with patients with COVID-19. Finally, it is worth highlighting primary effusion lymphoma-like lymphoma (PEL-LL), which is a possible complication of long-standing tuberculous pleuritis [21]. PELLL is a rare B-cell lymphoma characterized by the expression of pan B-cell markers (CD19, CD20, or CD 79a). Diagnosis of PELLL requires a long period of time because it follows a unique progression of disappearance and recurrence of the pleural effusion [21,22]. As a pleural biopsy was not performed, PEL-LL was not completely ruled out in the patient’s presentation.

Although chylothorax and pseudochylothorax are rare entities, they should be considered during the investigation of a patient with pleural fluid. The diagnosis of these effusions is important because each has different etiologies and management. Identifying the etiology can also help in the diagnosis and correct treatment of the underlying disease [5]. Cholesterol-rich effusions should be looked for during the analysis of the pleural fluid by analyzing the lipid content because this can aid in the diagnosis [5]. The management of patients with this type of pleural effusion can range from simple procedures, such as evacuatory thoracentesis, to more complex procedures, such as pleuroscopy with or without pleural drainage. The choice of procedure will depend on the symptoms, the amount of fluid, and the recurrence of pleural effusion after the initial thoracentesis.

Conclusions

Although pseudochylothorax is a rare condition, its possibility must always be kept in mind to avoid the risk of misdiagnosis. This becomes more relevant for clinicians, as the main causes of pseudochylothorax are benign conditions. When clinicians are faced with pleural lipid effusion, the differential diagnosis of chylothorax and pseudochylothorax must be made, especially in cases caused by thoracic duct obstruction due to malignancies, trauma, surgical procedures, superior vena cava thrombosis, and heart insufficiency. In addition to the classic milky appearance and machine-oil appearance, a chocolate-colored appearance should serve as a clue to the diagnosis of pseudochylothorax.