{'fraction_non_alphanumeric': 0.03219756173804314, 'fraction_numerical': 0.015317286652078774, 'mean_word_length': 5.153846153846154, 'pattern_counts': {'":': 0, '<': 1, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Pleural Effusion in Multiple Myeloma: A Liquid State

In this issue of Acta Haematologica , Byun et al. [5] characterize in a multicenter fashion the incidence, etiology, and diagnostic process performed in MM patients with pleural effusion. There is paucity of data on this topic given the rarity of this presentation. Out of nearly 600 patients, 80 patients had pleural effusion, and 7 of those patients (9%) had myelomatous pleural involvement. In contrast, the most common cause of pleural effusion in this study was a parapneumonic effusion. This study confirms previous reports in which pleural effusion was seen in <10% of myeloma patients, and in most patients it was due to other etiologies which included heart failure, renal failure, parapneumonic effusion, and amyloidosis. The presence of concomitant amyloidosis is a more likely cause of pleural effusion than MPE [6] , either from cardiac involvement (heart failure), renal involvement (nephrotic syndrome and hypoalbuminemia), hepatic involvement (ascites), or lung involvement. As the etiology of pleural effusion in the general population varies among geographic areas, this may also be reflected in the distribution of causes of pleural effusion among myeloma patients. However, myelomatous involvement of the pleural cavity should remain a relatively uncommon cause of pleural effusion. As the array of etiologies of pleural effusion in myeloma patients is wide, it seems justifiable to pursue the etiology of the pleural effusion. One should also keep in mind that the diagnostic workup is usually nonexhaustive and limited to advanced imaging (CT and PET-CT) and a thoracentesis (pleural tap). Multiple myeloma (MM) is a clonal plasma cell proliferative disorder and the second most common hematologic malignancy, with over 150,000 newly diagnosed patients per year worldwide [1] . The diagnosis of active MM is based either on the presence of the CRAB features (hypercalcemia, renal impairment, anemia, and bone lesions) in a symptomatic patient or on the presence of other myeloma-defining events in an asymptomatic patient, as was redefined by the International Myeloma Working Group (IMWG) in 2014. This represents a paradigm shift in the approach to myeloma in an attempt at early intervention in a subset of high-risk asymptomatic patients, destined to progress to active MM within 2 years, before the development of end organ damage [2] . Extramedullary disease (EMD), defined by the presence of clonal plasma cells outside the bone marrow, is not a common feature at presentation, with an incidence between 7 and 18% [3] . In relapsed-refractory disease it may be seen in up to 30% of patients [4] . Although EMD represents tumor independence of the bone marrow microenvironment and suggests a gain of invasion of aggressiveness by the tumor cells, the prognostic implication of EMD has not been consistently demonstrated. It appears, however, that plasmacytomas that are not continuous with a bony structure (i.e., soft-tissue plasmacytoma) are associated with a heightened adverse outcome compared to plasmacytomas arising from a bone. Received: June 19, 2017 Accepted: June 20, 2017 Published online: August 10, 2017