A 61-year-old male presents to your office with fever and dyspnea on exertion. He has been suffering from chronic, non-productive cough for 1 year. You note late inspiratory crackles on auscultation. Pulmonary function tests reveal an FEV1/FVC ratio of 90% and an FVC that is 50% of the predicted value. Which of the following would you most likely see on a biopsy of this patient's lung?

Linear immunofluorescence along alveolar basement membranes

A 36-year-old man presents with increasing shortness of breath for a month, which is aggravated while walking and climbing up the stairs. He also complains of pain and stiffness in both wrists, and the distal interphalangeal and metacarpophalangeal joints of both hands. He was diagnosed with rheumatoid arthritis 6 months ago and was started on methotrexate with some improvement. He is a lifetime non-smoker and has no history of drug abuse. The family history is insignificant for any chronic disease. The blood pressure is 135/85 mm Hg, pulse rate is 90/min, temperature is 36.9°C (98.5°F), and the respiratory rate is 22/min. Physical examination reveals short rapid breathing with fine end-inspiratory rales. An echocardiogram is normal with an ejection fraction of 55%. A chest X-ray shows diffuse bilateral reticular markings with multiple pulmonary nodules. Which of the following is the most likely cause of this patient’s lung condition?

Radiation-induced pulmonary disease

A 65-year-old male engineer presents to the office with shortness of breath on exertion and a dry cough that he has had for about a year. He is a heavy smoker with a 25-pack-years history. His vitals include: heart rate 95/min, respiratory rate 26/min, and blood pressure 110/75 mm Hg. On examination, he presents with nail clubbing and bilateral and persistent crackling rales. The chest radiograph shows basal reticulonodular symmetric images, with decreased lung fields. The pulmonary function tests show the following: diffusing capacity of the lungs for carbon monoxide (DLCO) is 43% and reference SaO2 is 94% and 72%, at rest and with exercise, respectively. What is the most likely diagnosis?

Chronic hypersensitivity pneumonitis

Pulmonary Langerhans cell histiocytosis

A 40-year-old woman comes to the physician for a 2-month history of chest pain and heartburn after meals. The patient reports that the pain is worse at night and especially when lying down. She has a history of Raynaud's disease treated with nifedipine. There is no family history of serious illness. She emigrated to the US from Nigeria 5 years ago. She does not smoke or drink alcohol. Vital signs are within normal limits. Cardiopulmonary examination shows no abnormalities. Thickening and hardening of the skin is seen on the hands and face. There are several firm, white nodules on the elbows and fingertips. Further evaluation of this patient is most likely to show which of the following findings?

Anti-RNA polymerase III antibodies

A 49-year-old woman comes to the physician because of a 4-month history of a dry cough and shortness of breath on exertion. She also reports recurrent episodes of pain, stiffness, and swelling in her wrist and her left knee over the past 6 months. She had two miscarriages at age 24 and 28. Physical examination shows pallor, ulcerations on the palate, and annular hyperpigmented plaques on the arms and neck. Fine inspiratory crackles are heard over bilateral lower lung fields on auscultation. Which of the following additional findings is most likely in this patient?

Decreased right atrial pressure

A 35-year-old female comes to the physician because of a 2-year history of progressive fatigue and joint pain. She has a 1-year history of skin problems and a 4-month history of episodic pallor of her fingers. She reports that the skin of her face, neck, and hands is always dry and itchy; there are also numerous “red spots” on her face. She has become more “clumsy” and often drops objects. She has gastroesophageal reflux disease treated with lansoprazole. She does not smoke. She occasionally drinks a beer or a glass of wine. Her temperature is 36.5°C (97.7°F), blood pressure is 154/98 mm Hg, and pulse is 75/min. Examination shows hardening and thickening of the skin of face, neck, and hands. There are small dilated blood vessels around her mouth and on her oral mucosa. Mouth opening is reduced. Active and passive range of motion of the proximal and distal interphalangeal joints is limited. Cardiopulmonary examination shows no abnormalities. Her creatinine is 1.4 mg/dL. The patient is at increased risk for which of the following complications?

Pulmonary arterial hypertension

A 37-year-old woman comes to the physician because of a 10-month history of excessive daytime sleepiness and fatigue. She says she has difficulty concentrating and has fallen asleep at work on numerous occasions. She also reports having frequent headaches during the day. She has no difficulty falling asleep at night, but wakes up gasping for breath at least once. She has always snored loudly and began using an oral device to decrease her snoring a year ago. She has occasional lower back pain, for which she takes tramadol tablets 1–2 times per week. She also began taking one rabeprazole tablet daily 3 weeks ago. She does not smoke. She is 175 cm (5 ft 7 in) tall and weighs 119 kg (262 lb); BMI is 38.8 kg/m2. Her vital signs are within normal limits. Physical and neurologic examinations show no other abnormalities. Arterial blood gas analysis on room air shows: pH 7.35 PCO2 51 mm Hg PO2 64 mm Hg HCO3- 29 mEq/L O2 saturation 92% An x-ray of the chest and ECG show no abnormalities. Which of the following is the most likely cause of this patient's condition?

Apneic episodes with obstructed upper airways

Chronic inflammatory airflow limitation

Thickening of alveolar membranes

Drug-induced respiratory depression

Diurnal alveolar hypoventilation

Interstitial lung disease classification for USMLE Step 1: High-Yield Internal Medicine Lessons

ILD Classification - The ILD Sorting Hat

Known Cause ILD:
- Connective tissue disease (e.g., RA, scleroderma)
- Drug-induced (e.g., Amiodarone, Bleomycin)
- Occupational (e.g., Asbestosis, Silicosis)
- Hypersensitivity Pneumonitis
Idiopathic Interstitial Pneumonias (IIPs):

HRCT chest: Basal, subpleural honeycombing in IPF

⭐ Usual Interstitial Pneumonia (UIP) is the hallmark radiologic and pathologic pattern of IPF, defined by bibasilar, subpleural honeycombing and reticulation. It carries the worst prognosis among the IIPs.

Idiopathic Interstitial Pneumonias - Alphabet Soup Pneumonias

A group of diffuse parenchymal lung diseases of unknown cause, distinguished by specific histopathologic patterns.
Idiopathic Pulmonary Fibrosis (IPF)
- Most common type; worst prognosis (median survival 3-5 yrs).
- Histology: Usual Interstitial Pneumonia (UIP) pattern.
- CT: Bibasilar, peripheral reticulation with honeycombing.
Non-specific Interstitial Pneumonia (NSIP)
- Better prognosis than IPF; strongly associated with connective tissue disease.
- Histology: Temporally uniform inflammation or fibrosis.
Cryptogenic Organizing Pneumonia (COP)
- Formerly BOOP; excellent response to steroids.
- Histology: Masson bodies (granulation tissue plugs in alveoli).
Smoking-Related ILDs
- RB-ILD & DIP: Accumulation of "smoker's macrophages"; improve with smoking cessation.

⭐ The UIP pattern is the indispensable hallmark for diagnosing IPF, signifying irreversible patchy fibrosis and architectural distortion (honeycombing).

Idiopathic Interstitial Pneumonias: Features Comparison

ILD of Known Cause - Connective Tissue Culprits

Systemic Sclerosis (SSc): The most common CTD to cause ILD.
- Pattern: NSIP (Non-Specific Interstitial Pneumonia) is the classic finding.
- Associated with anti-Scl-70 antibodies.
Rheumatoid Arthritis (RA):
- Pattern: UIP (Usual Interstitial Pneumonia) is the most common, mimicking IPF.
- Affects older males, smokers, with high rheumatoid factor (RF) titers.
Polymyositis/Dermatomyositis (PM/DM):
- Patterns: Can be NSIP or Organizing Pneumonia (OP).
- Strongly associated with anti-Jo-1 antibody (Antisynthetase Syndrome).
Sjögren's Syndrome & SLE:
- Sjögren's: LIP (Lymphocytic Interstitial Pneumonia) is characteristic.
- SLE: ILD is less common; presents with varied patterns.

⭐ While pleural disease is the most common overall pulmonary issue in RA, UIP is the most frequent ILD pattern and carries a poorer prognosis similar to IPF.

CT scans of ILD patterns: UIP, LIP, NSIP, OP

Granulomatous ILD - Lumpy, Bumpy Lungs

Chest X-ray: Bilateral hilar lymphadenopathy in sarcoidosis

Sarcoidosis: Multisystem disease with non-caseating granulomas.
- Features: Bilateral hilar lymphadenopathy, ↑ serum ACE, hypercalcemia.
- BAL fluid: ↑ CD4/CD8 ratio (>3.5).
Hypersensitivity Pneumonitis (HP): Immune reaction to inhaled organic antigens (e.g., mold, avian proteins).
- "Farmer's lung," "Bird fancier's lung."
- Poorly formed non-caseating granulomas.

⭐ In contrast to sarcoidosis, HP typically shows a lymphocytic alveolitis with a decreased CD4/CD8 ratio (<1.0) in BAL fluid.

High-Yield Points - ⚡ Biggest Takeaways

ILDs are broadly grouped by known causes (e.g., drugs, occupational) versus idiopathic interstitial pneumonias (IIPs).

Idiopathic Pulmonary Fibrosis (IPF) is the most common IIP, defined by a UIP pattern on HRCT, and carries the worst prognosis.

Connective tissue diseases (e.g., scleroderma, RA) are a major cause of secondary ILD.

Smoking-related ILDs include respiratory bronchiolitis-ILD (RB-ILD) and desquamative interstitial pneumonia (DIP).

Sarcoidosis is a key granulomatous ILD, classically presenting with bilateral hilar lymphadenopathy.

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