Hypersensitivity pneumonitis: an overlooked cause of cough and dyspnea

Figures & data

Figure 1. (a) Chest x-ray shows non-enlarged but asymmetric hilar opacities. (b) Axial view demonstrates mild bronchitis with mucoid impaction in several bronchi and several widened bronchi surrounded by inflammation and positive signet ring sign, suggestive of mild bronchiectasis.

Table 1. Clinical features of hypersensitivity pneumonitis.

Category	Acute	Subacute	Chronic
Clinical duration	4–48 hours	Weeks to four months	Four months to years
Symptoms	Fever, chills, diaphoresis, cough, chest tightness, dyspnea, hypoxemia, generalized body aches and myalgias, headache	Exertional dyspnea, cough, fatigue, weight loss, episodic flares	Exertional dyspnea, cough, fatigue, weight loss
Immuno-pathophysiology	Alveolitis from neutrophilic infiltration, immune complex deposition with fibrin, tiny granulomas	Classic histologic triad of subacute HP: interstitial infiltrate, bronchiolitis, formation of poorly-formed granulomas. Triad is present in up to 75% of cases [14]. Interstitial infiltrate is typically composed of plasma cells and lymphocytes	Lymphocytic infiltration and fibrosis, neutrophil-mediated destruction, often includes eosinophil and mast cell infiltration
High-resolution CT chest findings	Ground glass opacities (most common), reticulonodular pattern, confluent alveolar opacification	Ground glass opacities centrilobular nodules, air trapping	Irregular subpleural linear opacifications, traction bronchiectasis, air trapping, lobar volume loss, Interstitial fibrosis, honeycombing pattern, patchy emphysema
Prognosis	Good	Typically good	Poor (especially with presence of extensive fibrosis)
Treatment	Avoidance of offending agent. Systemic corticosteroids if symptoms progress despite antigen avoidance. Lung transplant in severe cases of chronic HP.

Symptoms, pathophysiology, natural history, and treatment are presented based on different stages of HP.

Costabel U, Bonella F, Guzman J. Chronic hypersensitivity pneumonitis. Clin Chest Med. 2012;33(1):151–163.

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