Mumps Parotitis: Unilateral vs Bilateral Presentation
Mumps can present with either unilateral or bilateral parotid gland swelling, and the clinical case definition explicitly includes both presentations without specifying exact percentages for each. 1
Clinical Presentation Pattern
The ACIP defines a clinical case of mumps as "acute onset of unilateral or bilateral tender, self-limited swelling of the parotid or other salivary gland lasting ≥2 days, without other apparent cause." 1 This guideline-level definition establishes that both presentations are recognized manifestations of mumps, but does not quantify the relative frequency of each.
Key Clinical Considerations
Parotitis Is Not Always Present
- Only 30-40% of mumps infections produce typical acute parotitis, while 15-20% are asymptomatic and up to 50% present with nonspecific or respiratory symptoms. 2, 3
- The absence of parotitis does not exclude mumps, as serious complications can occur without evidence of parotid involvement. 4
Unilateral Presentation Is Well-Documented
- Unilateral parotid swelling is an established presentation pattern explicitly included in the CDC case definition. 1
- Case reports document unusual unilateral presentations, including synchronous unilateral parotid and submandibular gland involvement. 5
- Mumps characteristically presents as "bilateral or unilateral swelling of the parotid gland" in clinical descriptions. 6, 7
Important Clinical Pitfall
The lack of specific percentage data in the medical literature does not diminish the clinical importance of recognizing unilateral presentations. Clinicians should not dismiss mumps based solely on unilateral involvement, as this is an accepted manifestation of the disease. 1 Laboratory confirmation with mumps IgM serology or viral isolation is preferred over clinical diagnosis alone, particularly because parotitis has multiple infectious and noninfectious causes. 1
The guideline literature consistently acknowledges both unilateral and bilateral presentations as valid clinical manifestations but does not provide specific epidemiological data quantifying the percentage of each presentation pattern.