# Clinical Cases: Restrictive Lung Diseases

## Case 1: Idiopathic Pulmonary Fibrosis

### Clinical Image
![High-resolution CT showing pulmonary fibrosis](case_01_image.jpg)
*Source: [Wikimedia Commons - IPF CT](https://commons.wikimedia.org/wiki/File:IPF_amiodarone.jpg) - CC BY 2.0*

### Case Presentation
A 67-year-old man presents with progressive exertional dyspnea over the past 18 months. He describes gradually worsening exercise tolerance, now becoming short of breath walking up a single flight of stairs. He has a dry, nonproductive cough. He has a 20 pack-year smoking history but quit 15 years ago. On examination, he has digital clubbing and fine, inspiratory "Velcro-like" crackles at both lung bases. Vital signs show respiratory rate 18/min and oxygen saturation 94% at rest, dropping to 86% with a 6-minute walk test.

Pulmonary function tests show FEV1 2.4 L (72% predicted), FVC 2.8 L (68% predicted), FEV1/FVC ratio 0.86 (normal), TLC 4.2 L (65% predicted), and DLCO 45% predicted. The pattern is restrictive (reduced TLC with preserved or elevated FEV1/FVC ratio) with markedly reduced diffusing capacity.

High-resolution CT chest reveals bilateral, predominantly basal and peripheral reticular opacities, honeycombing (clusters of cystic airspaces with thick walls), and traction bronchiectasis. This pattern of usual interstitial pneumonia (UIP) on CT, combined with the clinical presentation in a patient over 60 with no identifiable cause, is diagnostic of idiopathic pulmonary fibrosis (IPF) without need for surgical lung biopsy.

The pathophysiology involves repetitive alveolar epithelial injury leading to abnormal wound healing, myofibroblast activation, and excessive collagen deposition. This fibrosis reduces lung compliance (explaining restrictive physiology), thickens the alveolar-capillary membrane (reducing DLCO), and causes progressive destruction of lung architecture (honeycombing).

The patient is started on nintedanib, an antifibrotic tyrosine kinase inhibitor that slows the rate of FVC decline but does not reverse existing fibrosis. He is referred for pulmonary rehabilitation and evaluated for lung transplant listing. Corticosteroids are NOT indicated and may be harmful in IPF - an important distinction from other interstitial lung diseases. He is counseled on the poor prognosis, with median survival of 3-5 years from diagnosis.

### Key Learning Points
- IPF shows the UIP pattern on CT: basal/peripheral honeycombing, reticular opacities, traction bronchiectasis
- Pulmonary function shows restrictive pattern (low TLC, normal/high FEV1/FVC) with reduced DLCO
- "Velcro crackles" and digital clubbing are characteristic physical findings
- Antifibrotics (nintedanib, pirfenidone) slow decline but do not cure - corticosteroids are contraindicated
- Lung transplantation is the only potentially curative option for eligible patients

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## Case 2: Sarcoidosis with Bilateral Hilar Lymphadenopathy

### Case Presentation
A 32-year-old African American woman presents after an abnormal chest X-ray was found on routine pre-employment screening. She is asymptomatic except for mild fatigue. She has no respiratory complaints. On examination, she has erythema nodosum (tender red nodules on the anterior shins). Vital signs and oxygen saturation are normal.

Chest X-ray shows prominent bilateral hilar lymphadenopathy without parenchymal infiltrates (Stage I sarcoidosis). CT chest confirms bilateral hilar and mediastinal lymphadenopathy without lung parenchymal involvement. Pulmonary function tests are normal: FEV1 98% predicted, FVC 100% predicted, TLC 95% predicted, DLCO 90% predicted.

Laboratory evaluation shows elevated serum ACE level at 95 U/L (normal 8-52). Serum calcium is 10.8 mg/dL (high normal). 24-hour urine calcium is elevated at 380 mg. Ophthalmologic examination reveals asymptomatic anterior uveitis.

Bronchoscopy with endobronchial ultrasound-guided biopsy of a hilar lymph node is performed, revealing well-formed, non-caseating granulomas without evidence of infection or malignancy. Special stains and cultures for mycobacteria and fungi are negative. The diagnosis of sarcoidosis is confirmed.

Sarcoidosis is a multisystem granulomatous disease of unknown etiology. The non-caseating granulomas are composed of epithelioid histiocytes and multinucleated giant cells surrounded by lymphocytes. The disease can affect virtually any organ, but pulmonary involvement occurs in over 90% of cases.

Given her Stage I disease, lack of respiratory symptoms, and normal pulmonary function, the patient is managed with observation rather than treatment. Stage I sarcoidosis has a high rate of spontaneous remission (60-80%). Her ocular involvement requires topical corticosteroid drops. She is counseled to avoid excessive sun exposure and calcium/vitamin D supplements due to risk of hypercalcemia (granulomas produce 1,25-dihydroxyvitamin D). At 1-year follow-up, her hilar adenopathy has resolved spontaneously.

### Key Learning Points
- Sarcoidosis is characterized by non-caseating granulomas; infection must be excluded
- Pulmonary staging: Stage I (hilar nodes only), Stage II (nodes + parenchymal), Stage III (parenchymal only), Stage IV (fibrosis)
- Stage I has high spontaneous remission rate; treatment reserved for symptomatic or progressive disease
- Extrapulmonary manifestations include ocular (uveitis), skin (erythema nodosum, lupus pernio), cardiac, and neurologic
- Hypercalcemia results from granuloma production of 1,25-dihydroxyvitamin D

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## Case 3: Hypersensitivity Pneumonitis from Bird Exposure

### Case Presentation
A 55-year-old woman presents with progressive dyspnea and cough over 6 months. She notes that symptoms improve when she travels but worsen upon returning home. Detailed history reveals she has kept parakeets as pets for the past 3 years. On examination, she has fine inspiratory crackles throughout both lung fields. Oxygen saturation is 92% on room air.

Pulmonary function tests show FEV1 1.8 L (68% predicted), FVC 2.0 L (62% predicted), FEV1/FVC 0.90, TLC 3.5 L (58% predicted), and DLCO 52% predicted. The pattern is restrictive with reduced diffusing capacity. High-resolution CT chest shows diffuse ground-glass opacities, mosaic attenuation (areas of air trapping from small airway involvement), and centrilobular nodules - a pattern consistent with subacute hypersensitivity pneumonitis.

Bronchoalveolar lavage reveals lymphocytosis (55% lymphocytes, normal less than 15%) with a CD4/CD8 ratio of 0.6 (decreased, in contrast to sarcoidosis which shows elevated ratio). Serum precipitins to avian proteins are positive.

The diagnosis is bird fancier's lung, a form of hypersensitivity pneumonitis caused by immune-mediated reaction to avian proteins (found in droppings and feathers). The pathophysiology involves a combined type III (immune complex) and type IV (cell-mediated) hypersensitivity reaction in sensitized individuals.

The cornerstone of treatment is antigen avoidance - the patient rehomes her birds and undergoes professional cleaning of her home to remove accumulated avian proteins. She is started on a tapering course of prednisone given her significant functional impairment. At 3-month follow-up, her symptoms have markedly improved, DLCO has increased to 72% predicted, and CT shows resolution of ground-glass opacities. Had she continued exposure, she would have been at risk for progression to chronic fibrotic disease resembling IPF.

### Key Learning Points
- Hypersensitivity pneumonitis is an immune-mediated reaction to inhaled organic antigens
- Detailed exposure history is critical - symptoms improving away from home/work is a key clue
- CT findings include ground-glass opacities, mosaic attenuation, and centrilobular nodules
- BAL shows lymphocytosis with low CD4/CD8 ratio (opposite of sarcoidosis)
- Antigen avoidance is essential; continued exposure leads to irreversible fibrosis