Spotlight on the diagnosis of extrinsic allergic alveolitis (hypersensitivity pneumonitis)

Repeated inhalative exposures to antigenic material from a variety of sources, mainly from moulds, thermophilic Actinomycetes, and avians, respectively, can induce immune responses with the clinical picture of extrinsic allergic alveolitis (EAA) or hypersensitivity pneumonitis. Delays of years or even decades till the diagnosis is made are not uncommon; frequent misdiagnoses include allergic asthma, COPD, recurrent flue and other infections. We provide here the state of the art references, a detailed case description and recommend a current diagnostics schema.

1. 1.

   Case history: 4-8 hours following heavy exposure to an inciting agent patients develop fever, chills, malaise, cough, dyspnea, headache (acute course). Some cases don’t develop acute symptoms, rather, they have an insidious onset of these symptoms. Especially at lower exposures, patients gradually develop productive chronic cough, dyspnea on exertion, fatigue, anorexia, weight loss (subacute or intermittent course) (Table 2). These findings may be also present in patients who experience repeated acute attacks.

2. 2.

   Physical examination: During the acute attack there are fever, tachypnea, and diffuse fine bibasilar end-inspiratory crackles upon auscultation. Further frequent findings include muscle wasting, weight loss, in the chronic pronounced form also clubbing, tachypnea, respiratory distress.

3. 3.

   Lung function testing: A restrictive ventilatory pattern (i.e. reduced total lung capacity, vital capacity, and lung compliance) and impaired gas exchange parameters (reduced diffusing capacity, hypoxemia during exercise or even at rest) are typical features of the advanced chronic course. Also a mixed obstructive and restrictive ventilation pattern can develop.

4. 4.

   IgG antibodies and other laboratory findings: High serum concentrations of IgG antibodies specific for causative antigens are found in c. 70% of affected patients (Figure 2). More problematic from the diagnostic view is that more than 50% of the prevailing exposed healthy subjects may show such antibodies, depending on the causative antigen(s) and sensitivity and specificity of the laboratory test used. So far, for most causative antigens validated laboratory tests are not available on the market. In addition to an immunocomplex-mediated process, cell-mediated immunity obviously plays an important pathophysiological role. However, no routine diagnostic test for displaying this cellular response is available yet. Other abnormal laboratory findings during acute and subacute courses include leukocytosis, neutrophilia, elevated erythrocyte sedimentation rate, and increased levels of quantitative immunoglobulins and C-reactive protein.

5. 5.

   Radiological findings: The typical pictures are centrilobular micronodular (HRCT), patchy or reticular opacities which are mostly prominent in lower lung zones (Figure 3). Ground-glass opacities in the lower and middle lung zones and an interstitial pneumonitis-like pattern may be present during acute attacks. The end stage of the chronic course is characterized by fibrosis and even honeycombing predominant in the lower parts of the lungs. Emphysema may also occur [13].

6. 6.

   Serial lung function testing during antigen exposure periods and days off (exhibiting changes as outlined under SIC and restitution of symptoms and impaired lung function during days off).

7. 7.

   Specific inhalative challenge test (SIC): This is a laborious and time consuming diagnostic test by the use of the suspected causative agent. It should only be performed by well-experienced physicians. If done correctly it is a very sensitive and specific diagnostic method. See Table 2 and example in Figures. 1D, methodological methods have been published elsewhere [14,15], with the supplementary material from the European task force on SIC published online asthma additional Handbook of procedures for specific inhalation challenge testing http://erj.ersjournals.com/content/suppl/2014/03/07/09031936.00180313.DC1/Final_Handbook.pdf

8. 8.

   Bronchoalveolar lavage: Bronchoalveolar lavage shows leukocytosis (neutrophilia) in the alveoli and small airways in the acute course followed by an influx of mononuclear cells (Figure 1D). In the subacute and chronic courses lymphocytosis with increased CD8 + cells and a CD4+/CD8+ ratio of < 1 are observed 6 hours post challenge.

9. 9.

   Lung histology: Invasive diagnostics, i.e. lung biopsy, is usually not needed. In the acute course leukocytic inflammation is dominating. Lymphocyte-dominant interstitial inflammatory cell infiltration, well-formed interstitial epitheliod cell nonnecrotizing granulomas with giant cells are characteristic for the subacute and chronic courses. Cellular bronchiolitis and foci of bronchiolitis obliterans and intra-alveolar fibrosis may also occur. The chronic course includes an interstitial (organizing) pneumonia–like pattern with sub pleural patchy fibrosis, fibroblastic foci with centrilobular fibrosis, finally alveolar destruction (honeycombing) [16,17].

10. 10.

    Integrated diagnostic approach: Above steps 1 through 5 present basic routine diagnostics. If all of them exhibit concordant positive findings diagnosis of extrinic allergic alveolitis is sufficiently likely. If one or more of the respective 6 parameters is/are negative or equivocal at least one additional diagnostic procedure is needed, i.e. serial lung function testing during antigen exposure periods and days off (combined with follow-up of clinical symptoms) or specific inhalation challenge test, bronchoalveolar lavage or lung biopsy (Table 3).

    Full size table

Case 1 (farmers’ lung)

Case history: The 53 year old farmer has suffered for 5 years from cough, progressive shortness of breath during exertion, chills and fever in late evenings and nights during winter months. He always feed his 40 cows hay which was frequently mouldy.

Physical examination: Inspiratory crackles on basal lung fields.

Lung function testing: A restrictive ventilatory pattern (i.e. reduced total lung capacity, vital capacity, and lung compliance) and impaired gas exchange parameters.

IgG antibodies: High serum concentrations of IgG antibodies for aspergillus species and.

Specific inhalative challenge test (Figures. 1D) of this patient suffering from farmers’ lung by a probe of his mouldy hay (Figure 1A); for the outcome see Figure 4.

Radiological findings: Patchy opacities on both lower and middle lung fields.

Bronchoalveolar lavage: Bronchoalveolar lavage showed leukocytosis (neutrophilia) in the alveoli and small airways in the acute phase followed by an influx of mononuclear cells.

Case 2 (humidifier lung)

Figure 1C shows humidifier water of a printing plant where several heavily microbially contaminated humidifiers were installed and our 33 year old patient was employed. For chest x-ray findings see Figure 3.

Case history: He had complained of flu-like symptoms and chronic productive cough for more than 6 years without seasonal variation and increasing shortness of breath on exertion.

IgG antibodies: Serum IgG antibody analysis (Figure 2B) showed extremely high concentrations for the extract of the probe shown in Figure 1C, and lower concentrations for a variety of moulds and bacteria.

Specific inhalative challenge test: This was done by means of this humidifier water probe produced after a latency of 4 hours increasing cough, dyspnea, fever, a significant falls of vital capacity and arterial oxygen partial pressure, lasting for 3 hours.

Prevention and Treatment

The best outcome is offered by early recognition and consistent prevention of further exposures. To avoid the causative agent(s) is also the only effective measure to prevent relapses, the typically progressive disorder and permanently impaired lung function. Corticosteroids may be needed in cases with severe acute courses (starting with 0.5-1 mg prednisone/kg). Less sever acute courses abate without treatment.

Disclosure

XB testified in occupational diseases litigation on behalf of here described plaintiff cases and provide independent expert opinion for social courts or statutory insurances.

Affiliations

1. Institute for Occupational Medicine, Charité University Medicine Berlin, Berlin, Germany

   • Xaver Baur
   •  & Axel Fischer

2. Division Occupational Toxicology and Immunology, Institute for Occupational and Maritime Medicine (ZfAM), University Medical Center Hamburg-Eppendorf. University of Hamburg, Hamburg, Germany

   • Lygia T Budnik

3. European Society for Environmental and Occupational Medicine, EOM, Berlin, Germany

   • Xaver Baur
   • , Axel Fischer
   •  & Lygia T Budnik

Corresponding author

Correspondence to Xaver Baur.

Competing interests

The authors declare that they have no competing interests whether with a product company or a lobby group.

Authors’ contributions

XB, LTB, AF performed the literature review, XB examined the patients and provided the clinical data on cases; LTB supervised the laboratory analyses; XB, LTB drafted the manuscript; XB, AF, LTB edited and revised the manuscript. All authors read and approved the final manuscript.

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