Allergic bronchopulmonary mycosis caused by Bipolaris — SCE Respiratory MCQ

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HardAllergy and ImmunologyAllergic bronchopulmonary mycosis caused by BipolarisSCE Respiratory

A 46-year-old woman with adult-onset asthma has recurrent expectoration of tenacious brown mucus plugs despite high-dose inhaled corticosteroid/formoterol. Before receiving systemic corticosteroids, her blood eosinophil count was 0.92 × 10^9/L and serum total IgE was 760 IU/mL. Thin-section CT shows central bronchiectasis with branching mucus impaction; several plugs have attenuation greater than paraspinal skeletal muscle. Aspergillus fumigatus-specific IgE is repeatedly <0.10 kUA/L, skin-prick testing to A. fumigatus is negative, and IgE against recombinant Asp f1, f2 and f4 is undetectable. A. fumigatus-specific IgG is below the UK assay threshold. Three good-quality sputum samples collected over 6 weeks consistently grow Bipolaris species, without Aspergillus, pathogenic bacteria or mycobacteria. A validated specialist-laboratory assay demonstrates Bipolaris-specific IgE and IgG. She has no fever, immunosuppression, pulmonary cavitation or extrapulmonary disease. Which diagnostic classification is most appropriate?

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Correct answer: A — Allergic bronchopulmonary mycosis caused by Bipolaris

Explanation lettering: D = shown as A · A = shown as B · B = shown as C · C = shown as D

This is allergic bronchopulmonary mycosis (ABPM) caused by Bipolaris. She has the allergic bronchopulmonary disease phenotype: asthma, total IgE above the revised 500 IU/mL threshold, historical eosinophilia, bronchiectasis and high-attenuation mucus. However, repeated negative A. fumigatus-specific IgE, negative Aspergillus skin testing and absent recombinant Asp f1/f2/f4 responses argue strongly against ABPA. Repeated isolation of the same non-Aspergillus fungus, together with demonstrable sensitisation to that fungus, identifies the cause as Bipolaris. A is attractive because high-attenuation mucus is highly characteristic of allergic bronchopulmonary disease, but ABPA requires evidence implicating Aspergillus rather than another fungus. B is incorrect because severe asthma with fungal sensitisation does not account for the full immunological and radiological ABPM syndrome. C is plausible because Bipolaris was repeatedly cultured, but fungal bronchitis lacks the combination of marked total IgE elevation, fungal sensitisation, eosinophilia and characteristic mucus impaction. E cannot explain the coherent association between repeated Bipolaris isolation, Bipolaris-specific immune responses and allergic bronchopulmonary radiology. The radiological pattern establishes allergic bronchopulmonary mycosis; organism-specific testing determines whether it is ABPA or non-Aspergillus ABPM.

Reference: Revised ISHAM-ABPA working group clinical practice guidelines for diagnosing, classifying and treating allergic bronchopulmonary aspergillosis/mycoses (4 April 2024) — https://publications.ersnet.org/content/erj/63/4/2400061.full