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Pharyngitis for USMLE Step 1

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Pharyngitis for the USMLE Step 1 Exam
Etiology
  • Viral Causes:
    • The majority of pharyngitis cases are caused by viruses, including:
    • Rhinovirus: The most common cause of viral pharyngitis.
    • Adenovirus: Causes sore throat, fever, and conjunctivitis.
    • Influenza and Parainfluenza: Present with more systemic symptoms like fever and myalgias.
    • Epstein-Barr Virus (EBV): Causes infectious mononucleosis, with fever, sore throat, and posterior cervical lymphadenopathy.
    • Herpes Simplex Virus (HSV): May present with pharyngeal vesicles and ulcers.
  • Bacterial Causes:
    • Group A Streptococcus (GAS) (Streptococcus pyogenes) is the most common bacterial cause of pharyngitis, responsible for 20-30% of cases in children and 5-15% in adults.
    • Other bacterial causes include Neisseria gonorrhoeae and Corynebacterium diphtheriae (diphtheria).
Clinical Features
pharyngitis
  • Viral Pharyngitis:
    • Symptoms include sore throat, cough, rhinorrhea, hoarseness, and low-grade fever.
    • EBV (infectious mononucleosis) may present with severe sore throat, fever, fatigue, posterior cervical lymphadenopathy, and splenomegaly.
    • Adenovirus infection often includes conjunctivitis (pharyngoconjunctival fever).
  • Bacterial Pharyngitis (GAS):
    • Sudden onset of sore throat, high fever, and absence of cough.
    • Tonsillar exudates, tender anterior cervical lymphadenopathy, and palatal petechiae.
    • Scarlet fever may present with a fine, sandpaper-like rash and strawberry tongue.
    • Abdominal pain, headache, and nausea may also occur, especially in children.
Diagnosis
  • Clinical Scoring Systems:
    • The Centor criteria are used to assess the likelihood of GAS pharyngitis:
    • Tonsillar exudates, tender anterior cervical lymphadenopathy, fever, and absence of cough.
    • A score of 3 or higher warrants further testing.
  • Rapid Antigen Detection Test (RADT):
    • Detects GAS with high specificity. A positive result confirms GAS pharyngitis.
    • Negative RADT results in children should be followed by a throat culture.
  • Throat Culture:
    • Gold standard for diagnosing GAS pharyngitis. Performed if RADT is negative in children or if high suspicion persists in adults.
  • Monospot Test/EBV Serology:
    • Used to diagnose infectious mononucleosis in patients with symptoms of EBV (e.g., sore throat, fatigue, lymphadenopathy).
Management
Viral Pharyngitis
  • Supportive Care:
    • Viral pharyngitis is self-limiting. Symptomatic relief includes:
    • Analgesics (e.g., acetaminophen or ibuprofen) for pain and fever.
    • Throat lozenges and hydration to relieve sore throat.
    • Antibiotics are not indicated for viral pharyngitis.
  • EBV (Infectious Mononucleosis):
    • Supportive care includes rest and avoidance of contact sports (due to the risk of splenic rupture). Steroids may be used in severe cases (e.g., airway obstruction).
Bacterial Pharyngitis (GAS)
  • Antibiotics:
    • Penicillin V or amoxicillin is the first-line treatment. A 10-day course is recommended to prevent complications.
    • Alternatives for penicillin-allergic patients include azithromycin, clindamycin, or cephalexin.
  • Symptomatic Treatment:
    • Analgesics and antipyretics (e.g., ibuprofen, acetaminophen) are used to reduce fever and pain.
  • Prevention of Complications:
    • Early treatment reduces the risk of rheumatic fever and other complications.
Complications
  • Suppurative Complications:
    • Peritonsillar abscess: Presents with severe unilateral throat pain, trismus, and "hot potato" voice. Requires drainage and antibiotics.
    • Retropharyngeal abscess: Neck stiffness, dysphagia, and potential airway compromise. Requires surgical drainage.
  • Nonsuppurative Complications:
    • Rheumatic fever: Occurs weeks after untreated GAS infection, causing fever, arthritis, carditis, and chorea.
    • Post-streptococcal glomerulonephritis: Manifests with hematuria, edema, and hypertension after GAS infection.
Key Points
  • Pharyngitis is most commonly caused by viral infections such as rhinovirus, adenovirus, and EBV. Group A Streptococcus (GAS) is the most common bacterial cause.
  • Viral pharyngitis presents with mild sore throat, cough, and rhinorrhea, while bacterial pharyngitis (GAS) is characterized by high fever, tonsillar exudates, and tender anterior cervical lymphadenopathy.
  • Diagnosis of GAS pharyngitis is based on clinical scoring (Centor criteria) and confirmed with rapid antigen detection tests or throat cultures.
  • Treatment for viral pharyngitis is supportive, while GAS pharyngitis requires antibiotics (penicillin or amoxicillin) to prevent complications such as rheumatic fever and peritonsillar abscess.
  • Complications include peritonsillar abscess, retropharyngeal abscess, rheumatic fever, and post-streptococcal glomerulonephritis.

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