Pharyngitis for USMLE Step 3
Pharyngitis for the USMLE Step 3 Exam
Etiology
- Viral Causes:
- Most cases of pharyngitis are viral, accounting for 70-90% of adult cases. Common viral pathogens include:
- Rhinovirus: The most frequent cause.
- Adenovirus: Causes pharyngoconjunctival fever (sore throat, fever, conjunctivitis).
- Influenza and Parainfluenza: Often present with pharyngitis, cough, and systemic symptoms like fever and myalgia.
- Epstein-Barr Virus (EBV): Causes infectious mononucleosis, characterized by sore throat, posterior cervical lymphadenopathy, fever, and fatigue.
- Herpes Simplex Virus (HSV): Associated with vesicles or ulcers on the pharynx or tonsils.
- Bacterial Causes:
- Group A Streptococcus (GAS) (Streptococcus pyogenes) is the most common bacterial cause of pharyngitis, responsible for 5-15% of adult cases.
- Other bacterial causes include Neisseria gonorrhoeae (gonococcal pharyngitis), Corynebacterium diphtheriae, and Mycoplasma pneumoniae.
Clinical Features
- Viral Pharyngitis:
- Sore throat accompanied by cough, rhinorrhea, conjunctivitis, or hoarseness.
- EBV (infectious mononucleosis) presents with severe sore throat, fever, posterior cervical lymphadenopathy, fatigue, and splenomegaly.
- Bacterial Pharyngitis (GAS):
- Sudden onset of sore throat, fever, tonsillar exudates, and tender anterior cervical lymphadenopathy.
- Absence of cough or rhinorrhea.
- Scarlet fever may present with a fine, sandpaper-like rash and strawberry tongue.
Diagnosis
- Centor Criteria:
- Helps determine the likelihood of GAS pharyngitis based on the following:
- Tonsillar exudates (+1)
- Tender anterior cervical lymphadenopathy (+1)
- Fever (+1)
- Absence of cough (+1)
- Age: 3-14 (+1), 15-44 (0), >45 (-1)
- A Centor score of ≥3 suggests the need for further testing.
- Rapid Antigen Detection Test (RADT):
- Confirms GAS pharyngitis with high specificity. A positive result warrants antibiotic treatment. A negative RADT in children should be confirmed with a throat culture.
- Throat Culture:
- Gold standard for diagnosing GAS pharyngitis, particularly if RADT is negative in children or clinical suspicion remains high.
- EBV Testing:
- Heterophile antibody (Monospot) or EBV serology can confirm infectious mononucleosis.
Management
Viral Pharyngitis
- Supportive Care:
- Analgesics (e.g., acetaminophen or ibuprofen) for pain and fever relief.
- Hydration, throat lozenges, and saltwater gargles.
- Antibiotics are not indicated for viral causes of pharyngitis.
- EBV (Infectious Mononucleosis):
- Supportive care is key. Avoid contact sports due to the risk of splenic rupture. Corticosteroids may be used in severe cases (e.g., airway obstruction).
Bacterial Pharyngitis (GAS)
- Antibiotics:
- Penicillin V or amoxicillin is first-line therapy to reduce symptom duration, prevent complications, and reduce transmission. Alternatives for penicillin-allergic patients include cephalexin, clindamycin, or azithromycin.
- Symptom Management:
- Use analgesics for pain and fever control. Encourage hydration and rest.
Complications
- Suppurative Complications:
- Peritonsillar Abscess: Characterized by severe unilateral sore throat, trismus, uvular deviation, and a "hot potato" voice. Treatment includes drainage and antibiotics.
- Retropharyngeal Abscess: Presents with neck stiffness, dysphagia, and airway compromise, requiring surgical drainage and intravenous antibiotics.
- Nonsuppurative Complications:
- Acute Rheumatic Fever: A delayed complication of untreated GAS pharyngitis, presenting with fever, migratory arthritis, carditis, and Sydenham’s chorea.
- Post-streptococcal Glomerulonephritis: Manifests with hematuria, hypertension, and edema following GAS infection.
Key Points
- Pharyngitis is most commonly caused by viral pathogens, with Group A Streptococcus (GAS) being the primary bacterial cause.
- Viral pharyngitis presents with sore throat, cough, rhinorrhea, and conjunctivitis, while GAS pharyngitis presents with fever, tonsillar exudates, tender anterior cervical lymphadenopathy, and absence of cough.
- The Centor criteria guide the diagnosis of GAS pharyngitis, and confirmation is made with RADT or throat culture.
- Viral pharyngitis is treated with supportive care, while GAS pharyngitis requires antibiotics (penicillin or amoxicillin) to prevent complications like rheumatic fever.
- Complications of GAS pharyngitis include peritonsillar abscess, retropharyngeal abscess, rheumatic fever, and post-streptococcal glomerulonephritis.