Case In Point: A boy with shortness of breath, cough, and myalgias

The case

An 8-year-old boy presented with a 6-week history of shortness of breath, cough, and myalgias, but no fever. His pediatrician had made the diagnosis of bronchiolitis, and the patient was treated with azithromycin and albuterol via a metered-dose inhaler. Because the patient did not improve, he was given a 10-day course of amoxicillin, followed by a course of clarithromycin after a chest radiograph revealed bilateral infiltrates, suggesting atypical pneumonia.

The patient had no history of asthma, pneumonia, or recurrent otitis media. His sister received a diagnosis of bronchiolitis at the time of his diagnosis, but she improved after a course of azithromycin. His environmental history included the presence of dogs, a cat, a parakeet, and fish in the family home.

The patient and his family traveled to Mexico on vacation, by the end of which the patient's symptoms had improved. However, on the night that he returned home, he experienced dyspnea and cough. Hypoxia (oxygen saturation, 88%) was documented in the emergency department, and he required the administration of oxygen via nasal cannula at a rate of 0.25 L/min.

Chest auscultation revealed basilar crackles without wheezing. There was no evidence of club- bing or lymphadenopathy. Findings from a cardiac examination were negative. The patient denied any GI symptoms.

A chest radiograph showed bilateral perihilar and basilar infiltrates (Figure 1). Because of these findings and the presence of hypoxia (despite 3 courses of antibiotics), the patient was admitted to the pediatric department and the pediatric pulmonary service was consulted.

A high-resolution CT scan of the chest showed a diffuse ground-glass pattern with micronodules (Figure 2). Flexible bronchoscopy and bronchoalveolar lavage (BAL) demonstrated a nonerythematous tracheobronchial tree. Histopathologic results revealed 10% macrophages and 90% neutrophils. Cultures of BAL fluid were negative for bacteria, viruses, and fungi. The patient refused pulmonary function tests.

Results of a hypersensitivity panel for IgG antibodies, available a few weeks later, demonstrated high levels of IgG antibodies to bird feathers and pigeon droppings. Results of a sweat chloride test and immunoglobulin levels were normal. Based on clinical and radiologic findings, an initial diagnosis of hypersensitivity pneumonitis was made and was supported by the positive results for precipitating IgG antibodies.

Discussion

Because of its relatively low incidence, hypersensitivity pneumonitis is often misdiagnosed as respiratory infection or idiopathic interstitial lung disease,¹ depending on the patient's clinical presentation. There is no specific test for confirming hypersensitivity pneumonitis, and the diagnosis requires a high index of suspicion (Table).²

A diagnosis of hypersensitivity pneumonitis is less likely to be missed if environmental risks are routinely documented in patients with respiratory problems.³ An effort should be made to investigate any relationship between environmental exposure and onset of symptoms, as well as episodic clinical manifestations.

The diagnosis of hypersensitiv-ity pneumonitis is suspected when there is evidence of a respiratory disease in combination with a relevant history of environmental exposure. The suspicion is strengthened when there is a temporal relationship between symptoms and environmental exposure, as in our case, in which the patient's symptoms improved when travel kept him away from the bird and then worsened on reexposure.

In patients with hypersensitivity pneumonitis, the physical examination may reveal crackles and sometimes wheezing. Clubbing is uncommon. Routine laboratory tests may reveal a normal to moderately elevated erythrocyte sedimentation rate and leukocyte count. Peripheral eosinophil count and serum IgE concentration are generally normal, since the underlying histopathologic mechanism elicited by the offending allergen involves a cytotoxic delayed hypersensitivity reaction. Specific IgG serum precipitating antibodies help support the diagnosis.

Chest radiography and high-resolution CT scanning may provide supportive evidence.⁴ Findings vary according to whether the patient's disease is in an acute, subacute, or chronic stage.

In the acute stage, findings can include bilateral micronodules (1 to 4 mm in diameter), infiltrates, or patchy ground-glass opacities. In the chronic stage, the findings can include reticulonodular infiltrates, suggestive of interstitial fibrosis, and honeycombing.

Pulmonary function testing usually shows restrictive changes with impaired carbon monoxide-diffusing capacity. Superimposed airway obstruction may be seen, especially in chronic disease.

Analysis of BAL fluid usually reveals lymphocytosis, predominantly with CD8⁺ suppressor T cells, which supports the diagnosis. However, findings from BAL fluid analysis vary depending on the timing of the last antigen exposure and the disease stage. Neutrophils are predominant soon after an acute exposure; in our case, BAL was performed on the second day of the acute exposure. If the disease progresses to the chronic form, the lymphocyte count progressively increases, and when fibrosis is present, the number of neutrophils increases.

The mainstay of treatment of hypersensitivity pneumonitis is early diagnosis and the avoidance of further exposure to the causative agent(s). Supportive management and a course of corticosteroids may quicken the resolution of symptoms. The acute and subacute forms carry a good prognosis. However, the chronic form has a poor prognosis; patients are at risk for diffuse lung fibrosis that may be fatal.⁵

Outcome in this case

The family removed the bird from the home, and the patient began a 6-week course of oral corticosteroid therapy (prednisone at an initial dosage of 2 mg/kg for 2 weeks, with tapering over 4 weeks). Soon afterward, the patient's hypoxia resolved and his symptoms significantly improved. A follow-up visit 5 weeks later showed complete resolution of symptoms and normalization of chest radiographic findings.

References:

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