Pharyngitis for USMLE Step 2
Pharyngitis for the USMLE Step 2 Exam
Etiology
- Viral Causes:
- Most cases of pharyngitis are caused by viruses. Common viral pathogens include:
- Rhinovirus: The most frequent viral cause.
- Adenovirus: Associated with pharyngoconjunctival fever (sore throat, conjunctivitis, fever).
- Influenza and Parainfluenza: Present with pharyngitis alongside fever, myalgias, and cough.
- Epstein-Barr Virus (EBV): Causes infectious mononucleosis with sore throat, fever, and posterior cervical lymphadenopathy.
- Herpes Simplex Virus (HSV): Vesicles and ulcers on the pharyngeal mucosa, often severe in primary infections.
- Bacterial Causes:
- Group A Streptococcus (GAS) (Streptococcus pyogenes) is the most common bacterial cause of pharyngitis, responsible for 5-15% of adult cases and 20-30% of pediatric cases.
- Other bacteria: Include Neisseria gonorrhoeae (gonococcal pharyngitis) and Corynebacterium diphtheriae (diphtheria).
Clinical Features
- Viral Pharyngitis:
- Presents with sore throat, cough, rhinorrhea, and hoarseness. Low-grade fever and malaise are common.
- EBV (infectious mononucleosis): Severe sore throat, posterior cervical lymphadenopathy, fatigue, splenomegaly, and exudative pharyngitis.
- Adenovirus: Sore throat with conjunctivitis and fever.
- Bacterial Pharyngitis (GAS):
- Sudden onset sore throat with fever (>38°C), absence of cough, tonsillar exudates, and tender anterior cervical lymphadenopathy.
- Scarlet fever: Fine, sandpaper-like rash and strawberry tongue.
- Other symptoms: Headache, abdominal pain (more common in children), and nausea.
Diagnosis
- Centor Criteria:
- Predicts the likelihood of GAS pharyngitis based on clinical features:
- Tonsillar exudates, tender anterior cervical lymphadenopathy, fever, and absence of cough.
- A Centor score of 3 or higher warrants further testing.
- Rapid Antigen Detection Test (RADT):
- A positive test confirms GAS pharyngitis and warrants antibiotic treatment. Negative results in children should be confirmed with a throat culture.
- Throat Culture:
- The gold standard for diagnosing GAS pharyngitis. It is especially useful in children when RADT is negative.
- EBV Testing:
- Heterophile antibody (Monospot) test or EBV serology can confirm infectious mononucleosis.
Management
Viral Pharyngitis
- Supportive Care:
- Treatment includes rest, hydration, and symptomatic relief with:
- Analgesics (e.g., acetaminophen or ibuprofen) for pain and fever.
- Throat lozenges and saltwater gargles.
- Antibiotics are not indicated for viral infections.
- EBV (Infectious Mononucleosis):
- Supportive care, with avoidance of contact sports due to the risk of splenic rupture. Corticosteroids may be used for severe cases with airway obstruction.
Bacterial Pharyngitis (GAS)
- Antibiotic Therapy:
- First-line treatment is penicillin V or amoxicillin for 10 days. Alternatives for penicillin-allergic patients include cephalexin, clindamycin, or azithromycin.
- Early antibiotic treatment shortens symptom duration, reduces transmission, and prevents complications like rheumatic fever.
- Symptomatic Treatment:
- Analgesics (e.g., acetaminophen or ibuprofen) for pain and fever relief.
Complications
- Suppurative Complications:
- Peritonsillar Abscess: Presents with severe sore throat, trismus, and "hot potato" voice. Requires drainage and antibiotics.
- Retropharyngeal Abscess: Neck stiffness, dysphagia, and airway obstruction. Requires surgical drainage and intravenous antibiotics.
- Nonsuppurative Complications:
- Rheumatic Fever: A delayed complication of GAS pharyngitis, presenting with fever, arthritis, carditis, and Sydenham’s chorea.
- Post-streptococcal Glomerulonephritis: Occurs after GAS infection, manifesting with hematuria, edema, and hypertension.
Key Points
- Pharyngitis is commonly viral, with Group A Streptococcus (GAS) as the main bacterial cause. Differentiating viral from bacterial causes is essential for proper treatment.
- Viral pharyngitis presents with cough, rhinorrhea, and mild symptoms, while GAS pharyngitis presents with sudden onset of sore throat, fever, and tonsillar exudates.
- The Centor criteria help assess the likelihood of GAS pharyngitis, with rapid antigen detection tests and throat cultures used for diagnosis.
- Antibiotic therapy is essential for GAS to prevent complications like rheumatic fever. Viral pharyngitis is treated with supportive care.
- Complications include peritonsillar abscess, retropharyngeal abscess, rheumatic fever, and post-streptococcal glomerulonephritis.