Pigeon breeder’s disease as a cause of hypersensitivity pneumonitis in a child – A case report

INTRODUCTION

Hypersensitivity pneumonitis (HP) is an immune-mediated lung parenchymal injury that occurs due to chronic repeated inhalation of an offending antigen. Pigeon breeder’s disease is one of the most common forms of HP.^[1] However, it is less frequently reported in children. HP is most commonly diagnosed in children approximately 10 years of age,^[2] and 25% had a family history of the disease.^[3] We report a case of a 12-year-old boy presenting with chronic cough and progressive dyspnoea secondary to prolonged exposure to pigeons.

CASE REPORT

A 12-year-old male child, second born to a non-consanguineous couple, belonging to a low socioeconomic class and residing in an urban area, was brought to the emergency department with an acute onset of breathlessness for the past 2 h. He had a history of intermittent dry cough for the past 2 years, which aggravated during winter seasons, and progressive dyspnoea for the past 9 months. There are no prior wheeze episodes. There is no significant past or family history. Antenatal, perinatal, and birth history were uneventful. There is a significant history of exposure to pigeons in his bedroom for the past 3 years.

On examination, the child was obese (body mass index: 34.4 kg/m²). He had peripheral cyanosis, tachycardia, and tachypnoea. Oxygen saturation was 88% in room air, which improved to 98% with oxygen supplementation. Respiratory system examination revealed the use of accessory muscles of respiration and fine basal crepitations on both sides. Cardiovascular system, per-abdomen, and central nervous system examination were normal.

Arterial blood gas analysis showed a PaO₂ of 75 mmHg with respiratory alkalosis.

Chest X-ray revealed bilateral ground-glass haziness [Figure 1]. Spirometry showed a mixed ventilatory defect (obstructive and restrictive) with reduced diffusing capacity for carbon monoxide (DLCO). The values were as follows: Forced vital capacity (FVC) 38% predicted, forced expiratory volume in 1 s (FEV₁) 38% predicted, and FEV₁/FVC ratio of 99%, with significant post-bronchodilator response [Figure 2].

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Figure 1:

Posteroanterior view of chest X-ray: Bilateral ground glass opacities noted.

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Figure 2:

Spirometry showed a mixed ventilatory defect (obstructive and restrictive).

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High-resolution computed tomography (HRCT) of the chest showed extensive ground-glass opacification with focal areas of lucency/air trapping diffusely involving bilateral lungs. A few patchy areas of pneumonitis/sub-segmental atelectasis in the basal segments of the bilateral lower, right middle, and left lingular lobes were noted, suggestive of HP [Figures 3a and b].

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Figure 3:

(a) High-resolution computed tomography: Pointers showing diffuse air trapping in bilateral lung fields. (b) Red pointer: Showing bilateral ground glass opacities. Black point: Air trapping with traction bronchiectasis. (a) Red pointer: Bilateral Ground glass opacities are seen in lung field. Blacks pointer: Bilateral air trapping with traction bronchiectasis. (b) Black pointers: bilateral air trapping with traction bronchiectasis.

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Laboratory investigations revealed haemoglobin of 13.9 g/dL, C-reactive protein of 3.8 mg/L, platelet count of 4.26 lakh/mm³, total leucocyte count of 14,660/mm³ with neutrophils constituting 67.1%, and an absolute eosinophil count of 330/mm³.

Specific antigen testing or (bronchoalveolar lavage)/lung biopsy was not performed due to resource constraints.

A paediatric pulmonologist’s opinion was taken, and he was started on oral corticosteroids along with supportive management. Parents were counselled about the disease, avoidance of offending antigen by complete cessation of pigeon exposure and environmental modifications. His symptoms subsided with this treatment. Hence, oral steroids were continued for 1 month and followed up. As the child responded well and improved clinically, corticosteroids were tapered and stopped.

DISCUSSION

HP is a complex immune-mediated lung disorder, also referred to as extrinsic allergic alveolitis.^[4] It is a nonimmunoglobulin E-mediated immunological disease caused by chronic exposure to various antigens such as animal proteins, fungi, amoeba, bacteria, metals, and chemicals.^[5,6] Pigeon breeder’s disease is one of the most common causes of HP in children and results from inhalation of avian protein antigens present in pigeon feathers, droppings, and serum.

HP was first described as ‘farmer’s lung’ in 1713 among cereal workers.^[6] Among the various types of HP, pigeon breeder’s disease accounts for approximately 6–20% of cases, while farmer’s lung contributes to 1–9%, making it the most common form of HP.^[6,7]

The pathogenesis of HP involves a Th1-mediated type III and type IV hypersensitivity reaction following repeated exposure to inhaled antigens in a genetically susceptible host.^[8] Both environmental and genetic factors play a role in disease development. Chronic exposure leads to inflammatory and pathological changes mainly in the interstitium, alveoli, and terminal airways.

Clinically, HP is characterised by dyspnoea, chronic cough, fatigue, anorexia, chest pain, fever, chills, headache, and weight loss after chronic exposure to the antigens.^[8]

In our case, the child being obese is a confounding factor. Despite this, HP was diagnosed based on environmental exposure history, which was supported by imaging.

Pulmonary function tests typically reveal a restrictive pattern of lung disease with reduced DLCO. HRCT of the chest in chronic HP may show fibrotic changes, ground-glass opacities, centrilobular nodules, honeycombing, and traction bronchiectasis.^[4]

Diagnostic criteria for hypersensitivity pneumonia include six major and three minor criteria [Table 1].^[9] Establishing a diagnosis requires the presence of at least 4 major and 2 minor criteria. In our case, 4 major (symptoms compatible with HP, evidence of exposure to appropriate antigen by history {pigeons}, findings compatible with HP on chest radiograph or HRCT, positive natural challenge) and 2 minor (bibasilar rales, arterial hypoxia at rest) criteria are fulfilled. Treatment for chronic HP includes oral prednisolone over several months, depending on the response and improvement in symptoms and functional abnormalities, and prevention of exposure to the causative antigen.^[4]

HP is relatively uncommon in children and is often underdiagnosed due to its non-specific clinical presentation. It frequently mimics more common respiratory illnesses such as asthma, pulmonary tuberculosis, and other connective tissue disorders, including sarcoidosis, leading to diagnostic delay.^[10]

In our case, the child was initially thought to have asthma based on a history of exposure to allergens, use of an inhaled bronchodilator for the past 2 years, and a mixed ventilatory defect on spirometry. However, asthma was excluded by exposure history, lack of sustained bronchodilator response, and imaging findings.

We report this case to highlight pigeon breeder’s disease as an important and potentially reversible cause of HP in children when diagnosed early and treated appropriately. Management includes oral corticosteroids along with strict avoidance of the offending antigen; in this case, exposure to pigeons. Strict environmental measures were undertaken in our case, along with supportive measures, which were re-ensured during follow-up, resulting in symptomatic improvement with no further aggravation of symptoms.

In our case, on 1-year follow-up, there was a significant improvement in symptoms with no further exacerbations and demonstrable improvement in pulmonary function tests (FVC – 88% predicted, FEV₁ – 86% predicted and FEV₁/FVC ratio of 97.7%) (post-treatment follow-up imaging was not done due to financial constraints), which emphasises the importance of early recognition and timely intervention. Early diagnosis and prompt discontinuation of antigen exposure are crucial, as continued exposure can lead to irreversible pulmonary fibrosis and long-term morbidity like chronic lung disease.

CONCLUSION

Treating paediatricians should have a high index of suspicion for HP in children presenting with chronic cough, progressive dyspnoea, and a history of environmental exposure if not responding to conventional treatment. We emphasise the importance of thorough history taking, which plays a vital role in diagnosis and management, which can prevent unnecessary investigations, delays in treatment, and complications such as disease progression and irreversible lung damage.