Disease: Pulmonary Histiocytosis X

Clinical Information:

This 42 year old Caucasian male had a 2-year history of non-productive cough, dyspnea on exertion, and fatigue. He had four episodes of fever in the preceding 18 months. He had a 40 pack-year history of smoking. He was an airline pilot with no relevant past medical history, family history, occupational or domestic antigen exposures. Pulmonary function testing revealed a mild restrictive pattern.

Imaging:

His CXR shows a bilateral, predominantly mid- and upper-zone reticulonodular pattern with some small cystic areas in the upper lobes. There is mild bilateral hilar adenopathy.

Conventional and high resolution CT reveal multiple small nodules thin-walled, irregular cysts predominantly in the upper 1/3 of the lungs.

Discussion:

The combination of nodules and multiple, irregular-shaped, thin-walled cysts is highly suggestive of Pulmonary Histiocytosis X(also known as Pulmonary Eosinophilic Granulmona.This condition of unknown etiology is uncommon, occurring predominantly in smokers ( >90%) with mean age at presentation of 32 years. Patients may be asymptomatic (approx. 25%), or have non-specific respiratory symptoms . Pneumothorax is the presenting feature in up to 20%. Constitutional symptoms of fever, weight loss and fatigue may be present. Hemoptysis is rare, as is bone involvement in patients with pulmonary manifestations. Pulmonary function tests are non-diagnostic with normal, restrictive, obstructive, or mixed patterns all seen. Variable clinical course with spontaneous remissions and 2-6 % mortality. Presentation at extremes of age, multi-organ involvement, low diffusion capacity and recurrent pneumothoraces are independent poor prognostic indicators. Treatment is largely symptomatic.

Differential Diagnosis (DDx):

The recognized features of Pulmonary Histiocytosis X are 1- 5mm nodules and multiple thin-walled cysts which tend to coalesce to form bizarre shapes in a centrilobular/peribronchiolar distribution with an upper lung predominance. Intervening lung is often normal. Less commonly one may see cavitation in larger nodules, lymphadenopathy, ground-glass opacity or fine reticular opacity.

True lung cysts need to be distinguished from emphysematous blebs / bullae ( no visible walls), dilated airways (continuity and elongation of dilated airways on contiguous slices) and pneumatoceles.

The differential for true lung cysts lies between Histiocytosis X, Lymphangiomyomatosis (L.A.M.)and Tuberous sclerosis (T.S.). HRCT features may be identical in these patients. Helpful differentiating features are nodules and bizarre-shaped cysts with an upper lung predominance in Histiocytosis X, while LAM is associated with chylous effusions, female of child-bearing age, and more uniformly shaped cysts in a diffuse distribution. TS lung disease appears very similar to LAM but can be seen in males.

End-stage Idiopathic pulmonary fibrosis may occasionally cause confusion with extensive basal and subpleural honeycombing but the intervening lung is abnormal and fibrotic. In Histiocytosis X and LAM, the intervening lung is usually normal.

References:

Soler P. et al. Pulmonary Langherans' Cell Granulomatosis. Annu. Rev. Med. 1992;105-115.

Schonfield N. et al. Clinical and Radiographic Features, Lung Function and Therapeutic Results in Pulmonary Histiocytosis X. Respiration.1993; 60: 38-44.

Moore AD et al. Pulmonary Histiocytosis X: comparison of radiographic and CT findings. Radiology. 172(1) : 249-54, 1989 July.

Brauner MW et al. Pulmonary Histiocytosis X : evaluation with high-resolution CT. Radiology . 172 (1) : 255-8, 1989 Jul.

Case contributed by Martin O'Driscoll, MB and Debra Dyer, MD.


Debra Dyer, MD