Medical Mystery of the Week

       You are still practicing telemedicine. You are shown the chest x-ray and the results of a diagnostic thoracentesis of a 45-year-old man with a long history of joint pains.
      DIAGNOSIS: Rheumatoid arthritis (RA) with a rheumatoid pleural effusion.
      The most common extra-articular manifestations of RA involve the lung and/or pleura. These may include interstitial lung disease, pleural effusions, cricoarytenoiditis, constrictive or follicular bronchiolitis, bronchiectasis, pulmonary vasculitis, and pulmonary hypertension.
      Rheumatoid pleural effusions are most common in middle-aged men. Although usually transient and small, they may be large and persistent as in the presented case. Untreated, they may cause an ipsilateral fibrothorax.

       The chest x-ray shows a large left-sided pleural effusion and a small area of consolidation in  the right lower or middle lobe (left image). A microscopic view of the patient's pleural fluid shows a classic "comet cell" - a comet-shaped fusion of epithelial cells - as well as leukocytes and cellular debris. The effusion also contains high levels of rheumatoid factor and immune complexes, and a characteristically low pH and glucose level (right image).