Maple bark disease

Last revised by Craig Hacking on 10 Jun 2020

Maple bark disease, also known as maple bark stripper’s disease, is a rare hypersensitivity pneumonitis caused by the allergenic fungal spores of Cryptostroma corticale. The fungus causes sooty bark disease under the bark of maples and sycamore trees.

The first formal clinical accounts of the disease formed the original descriptions of hypersensitivity pneumonitis which was initially termed extrinsic allergic alveolitis. Timber workers in 1932 from the United States described symptoms related to exposure of an allergenic fungus on maple bark 1.

It presents as an acute pulmonary illness with cough, fever and dyspnea. Weight loss has been described. Clinical features are consistent with other forms of hypersensitivity pneumonitis and as is typical, removal of the patient from the allergenic environment causes resolution of symptoms. Emanuel et al. 2 describes a higher prevalence in winter months, likely due to reduced ventilation and increased exposure.

The lung demonstrates interstitial pneumonitis and granulomatous infiltration. Fungal spores may be cultured from lung biopsy or bronchoscopic washings.

CXR and chest CT show typical features of hypersensitivity pneumonitis, particularly involving the lower and mid zones. Radiographic resolution is expected following the removal of the patient from the allergenic environment.

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