What is the most likely diagnosis—cystic fibrosis, pneumonia, or pulmonary embolism—in a thin, malnourished Central American teenager with chronic purulent sinus discharge, wheezing, dyspnea, persistent cough, recurrent diarrhea since infancy, low‑grade fever, apical crackles, digital clubbing, increased anteroposterior chest diameter, right upper quadrant abdominal tenderness, chest imaging showing interstitial markings, mucus plugging and bronchiectasis, and abdominal imaging showing gallstones?

Cystic Fibrosis is the Diagnosis

This clinical presentation is pathognomonic for cystic fibrosis (CF), not pneumonia or pulmonary embolism. The constellation of chronic symptoms since infancy, malnutrition, digital clubbing, bronchiectasis, and gallstones in a teenager creates an unmistakable pattern that demands immediate CF diagnostic workup.

Why Cystic Fibrosis

The patient exhibits the classic multisystem manifestations of CF that distinguish it from acute processes like pneumonia or PE:

Respiratory Features Consistent with CF

• Chronic purulent sinus discharge and sinusitis - virtually all CF patients develop chronic sinusitis due to dehydrated mucosal fluids and viscous secretions 1
• Bronchiectasis on imaging - a hallmark of CF resulting from chronic infection/inflammation cycles 2
• Mucus plugging - pathognomonic for defective CFTR chloride channel function causing abnormally thick mucus 3, 2
• Digital clubbing - indicates chronic pulmonary disease progression 4
• Increased AP chest diameter - suggests chronic air trapping and hyperinflation from obstructive lung disease 2
• Apical crackles - consistent with bronchiectasis and chronic infection 4

Gastrointestinal Features Specific to CF

• Recurrent diarrhea since infancy - indicates pancreatic insufficiency with fat malabsorption, present in >80% of CF patients at diagnosis 3, 2
• Malnutrition and thin body habitus - direct consequence of pancreatic enzyme deficiency causing protein and fat malabsorption 3, 2
• Gallstones in a teenager - uncommon in this age group but well-documented in CF, though typically pigment stones rather than cholesterol 5
• Right upper quadrant tenderness - may indicate biliary disease or hepatic involvement, both CF complications 2

Timeline Excludes Acute Processes

The symptoms since infancy with chronic progression definitively rule out pneumonia (acute infection) and pulmonary embolism (acute thrombotic event). CF is a chronic genetic disease with manifestations beginning in early childhood 3, 2.

Diagnostic Confirmation Required

Order a sweat chloride test immediately - this remains the gold standard diagnostic test 1, 6. Chloride levels >60 mEq/L in children are diagnostic when combined with clinical features 1. The test requires collection of at least 75 mg of sweat via pilocarpine iontophoresis 1.

Obtain CFTR genetic testing - particularly important given the patient's Central American ethnicity 3. While CF is less common in Hispanic populations (1/4,000-10,000 births vs. 1/2,500-3,500 in non-Hispanic whites), it absolutely occurs and may involve different mutation patterns 3. The ΔF508 mutation accounts for two-thirds of CF alleles worldwide but is less frequent in non-European populations 3.

If Sweat Test is Intermediate (30-59 mEq/L)

Refer to a CF specialty center for advanced bioassays of CFTR function including nasal potential difference or intestinal current measurement 6. Some patients with milder mutations present with atypical phenotypes and intermediate sweat values 7, 6.

Why Not Pneumonia

Pneumonia is an acute infectious process that:

• Develops over days, not years since infancy
• Responds to appropriate antibiotic therapy within 1-2 weeks
• Does not cause chronic malnutrition, digital clubbing, or bronchiectasis
• Does not explain gallstones or chronic diarrhea

The low-grade fever and purulent secretions could represent a CF pulmonary exacerbation (acute worsening superimposed on chronic disease), but the underlying diagnosis is CF, not simple pneumonia 8, 9.

Why Not Pulmonary Embolism

PE is an acute thrombotic event that:

• Presents with sudden-onset dyspnea, pleuritic chest pain, and hemoptysis
• Does not cause chronic symptoms since infancy
• Does not produce bronchiectasis, mucus plugging, or digital clubbing
• Does not explain malnutrition, diarrhea, sinusitis, or gallstones
• Would be extraordinarily rare in a teenager without major risk factors (malignancy, thrombophilia, immobility)

While CF patients may have slightly increased PE risk due to chronic inflammation and immobility during exacerbations 10, the clinical picture here is chronic CF lung disease, not acute PE.

Critical Management Implications

Immediate referral to a CF specialty center is mandatory 2, 11. This patient requires:

• Comprehensive CFTR mutation analysis to guide potential modulator therapy 11
• Sputum culture for CF-specific pathogens (Pseudomonas aeruginosa, Staphylococcus aureus, Burkholderia cepacia) 1, 12
• Pancreatic enzyme replacement therapy for malabsorption 3, 2
• Aggressive nutritional rehabilitation with high-calorie diet and fat-soluble vitamin supplementation 2, 13
• Airway clearance therapy and mucolytics 4, 13
• Treatment of current pulmonary exacerbation with prolonged antibiotics (3-6 weeks minimum) 1

Common Pitfall to Avoid

Do not dismiss CF based on ethnicity alone. While less common in Hispanic populations, CF absolutely occurs and may present with atypical mutations 3. The clinical syndrome here is unmistakable regardless of ethnic background. Missing this diagnosis condemns the patient to progressive respiratory failure without access to life-extending therapies including CFTR modulators that have transformed CF prognosis 11.

The median survival for CF has improved to 46.2 years with early diagnosis and specialized multidisciplinary care 11. Delayed diagnosis in adolescence represents a critical missed opportunity for years of preventive therapy.