Non-Obstructive Middle Lobe Syndrome: An Unusual Cause of Recurrent Pneumonia in an Elderly Woman

An 84-year-old woman had five episodes of pneumonia in 4 months. Despite extensive comorbidities and advanced age, her health status was good and the recurrence seemed unjustified. Exhaustive background investigation revealed 14 episodes of right-sided pneumonias during the 3 previous years and an inconclusive investigation with CT of the thorax and bronchofibroscopy, despite some fibrotic and atelectasic alterations in the right middle lobe. A new right-sided x-ray showed a wedge-shaped density extending anteriorly and inferiorly from the hilum, and CT of the thorax revealed aggravated middle lobe abnormalities with thickening of the bronchial wall and segment atelectasis, without any visible airway obstruction. After extensive work-up had excluded other causes of recurrent pneumonia and immunodeficiency, a non-obstructive middle lobe syndrome (MLS) was deemed responsible for the repeated episodes of pneumonia. MLS is characterised by chronic hypoventilation and atelectasis of the middle lobe, facilitating secretion accumulation, chronic inflammation and repeated infection. After treatment with bronchodilators and immunostimulants was initiated, the patient experienced no recurrences for several months. LEARNING POINTS: Recurrent pneumonia is common and has several possible causes. Investigation should be directed by whether or not the location of the episodes varies, suggesting a systemic condition or a local abnormality, respectively. Middle lobe syndrome (MLS) is characterised by chronic hypoventilation of the right middle lobe resulting in atelectasis and secretion accumulation, sometimes causing recurrent pneumonia, and should therefore be considered in the differential diagnosis. MLS is not unusual in children with asthma but is quite uncommon in the elderly despite age-related changes in the characteristics of airways with reduced elastic recoil and mucociliary clearance.