CRYPTOGENIC ORGANIZING PNEUMONIA
Cryptogenic organizing pneumonitis (COP) is a specific clinicopathologic syndrome of unknown cause. The incidence and prevalence of COP are unknown, but a cumulative incidence of six to seven per 100,000 hospital admissions was found at a major teaching hospital. The disease onset is typically in the fifth or sixth decades of life, with men and women being affected equally.
The clinical presentation of COP often mimics that of
community-acquired pneumonia. In 50% of cases, the onset is heralded by a
flulike respiratory illness that includes fever, malaise, fatigue, and cough.
Almost three-fourths of patients have their symptoms for less than 2 months,
and few have symptoms for more than 6 months before diagnosis. Weight loss of
greater than 10 lb is seen in more than 50% of patients. Inspiratory crackles
are frequently present on chest examination. A normal pulmonary examination is
found in 25% of subjects.
Routine laboratory studies are nonspecific. A
leukocytosis without increase in eosinophils is seen in approximately half of
patients. The initial erythrocyte sedimentation rate is frequently elevated in
patients with COP.
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Pulmonary function is usually impaired with a restrictive
defect being most common. Resting and exercise arterial hypoxemia is common.
The radiographic manifestations are quite distinctive.
Bilateral, diffuse alveolar opacities in the presence of normal lung volume
constitute the characteristic radiographic appearance in patients with COP. The
alveolar opacities may rarely be unilateral. High- resolution computed
tomography (HRCT) scans of the lung reveal patchy airspace consolidation,
ground-glass opacities, small nodular opacities, and bronchial wall thickening
and dilatation. These patchy opacities occur more frequently in the periphery
of the lung and are often in the lower lung zone. The computed tomography (CT)
scan may reveal much more extensive disease than is expected by review of the
plain chest radiographs. Recurrent and migratory pulmonary opacities are
common.
Histopathologic organizing pneumonia is a specific
morphologic pattern of intraluminal fibrosis that is relatively nonspecific but
may be characteristic of certain
clinical syndromes. The lesion is characterized by excessive proliferation of
granulation tissue within small airways (proliferative bronchiolitis) and
alveolar ducts associated with chronic inflammation in the sur- rounding
alveoli. Foamy macrophages are commonly seen in the alveolar spaces, presumably
secondary to the bronchiolar occlusion. A uniform, temporally recent appearance
to the changes without severe disruption of the lung architecture is a characteristic finding. The
architecture of the lung is preserved, with no remodeling or honeycombing
found.
Corticosteroid therapy is the most common treatment
used in these patients. It results in clinical recovery in two-thirds of the
patients. Early reduction in the dose or cessation of initial orticosteroid
therapy may increase the risk
of relapse.
