Iodide mumps, a swelling of the salivary glands after iodinated contrast dye, is usually described as harmless and short-lived. But a 37-year-old woman's glands swelled so severely after a brain-vein procedure that she needed a breathing tube and a ventilator for three days.
The case report in the American Journal of Case Reports, by a University of Wisconsin–Madison neurologist and a colleague, was published online in February. It is one of several reports on the condition this year, including one that followed facial iodine iontophoresis, a treatment that uses electric current to push iodine through the skin. Its authors argue the reaction is likely underreported and that clinicians should keep it in mind when a patient's neck swells after a contrast procedure.
Swelling Within Hours of a Brain Procedure
The woman had idiopathic intracranial hypertension, a condition of raised pressure around the brain. She underwent a cerebral angiogram, followed a week later by venous sinus stenting. Each procedure used about 170 milliliters of iopamidol, an iodinated contrast agent.
About three hours after the stenting, her right parotid and submandibular glands, the salivary glands in front of the ear and under the jaw, became painfully swollen. Swallowing hurt, her breathing grew progressively harder, and she began using accessory muscles to breathe. Doctors intubated her and kept her on a ventilator for three days. CT imaging confirmed swelling of the right parotid and submandibular areas.
She was treated with medicines including methylprednisolone, diphenhydramine, and epinephrine, followed by dexamethasone and a two-week steroid taper, and her swelling substantially resolved. Her kidney function stayed normal throughout, with a creatinine of 0.8 mg/dL.
The iodine load was substantial. The authors estimated that the 171 milliliters of contrast used during stenting contained about 8,550 micrograms of free iodine, more than 50 times the minimum daily intake. Contrast agents are designed to hold iodine tightly, but a small free fraction still enters the bloodstream.
Normal Kidneys Don't Rule It Out
Iodide mumps has long been linked to reduced kidney function. According to the report, about 98% of iodine is cleared by the kidneys, so slower clearance can leave more circulating iodine for glands to absorb. The authors note that salivary glands "have the capacity to concentrate iodine to levels 20 to 100 times higher than those in serum," and excess iodine may trigger inflammation there.
Kidney trouble is not a prerequisite. Citing a 2020 meta-analysis of published cases, the authors report that only 39% of patients had a creatinine above 1.1 mg/dL. Cases have ranged in age from 8 to 80, with a median of 63, and about 85% involved swelling on both sides. This woman's swelling was on one side only.
The condition was first described in 1956. As of 2020, only 77 confirmed case reports had been documented, even though more than 75 million doses of iodinated contrast have been given worldwide, the authors wrote.
A Reaction That May Be Missed
The authors point to evidence that the low count may partly reflect missed diagnoses. They cite an observational study in which "otolaryngology providers trained to identify the condition detected 4 cases in 2 months, whereas emergency physicians without specialized training identified 0 cases" in the same population.
Because the swelling can appear hours after a scan, it can be mistaken for an infection, a salivary stone or an allergic reaction. A Radiology teaching case shows how CT can reveal symmetric enlargement of the glands without cysts or focal lesions. Repeat episodes have also been described, including recurrent iodide mumps after repeated contrast,reported in the Annals of Internal Medicine.
Prevention remains uncertain. Sour candy, hydration and saline gargles have been suggested, the authors wrote, "although none have demonstrated a clear benefit in reducing symptom duration."
Allergy Testing Pointed to One Specific Dye
The Wisconsin case adds a twist to the usual explanation. Iodide mumps is generally thought to result from iodine buildup rather than a classic allergy, and this patient did not have the low blood pressure, rash, or hives that mark anaphylaxis.
Yet her skin prick test was strongly positive for iopamidol, while tests for iohexol, another iodinated agent, were negative. The authors interpreted this as a selective sensitivity to iopamidol. They wrote that targeted skin testing can help "identify specific contrast agents that triggered the reaction and thus guide the selection of safer alternatives for future imaging."
That matters because contrast scans are often essential, and a broad "contrast allergy" label could keep someone from needed imaging. In this patient, the testing points to iohexol as a possible safer option, though the report does not describe her receiving it.
A single case cannot settle how iodide mumps works, and most episodes resolve on their own within days. Anyone who notices swelling under the jaw or in front of the ears after a contrast scan should contact a clinician. Trouble breathing or swallowing needs emergency care.
Key Questions Answered
What is iodide mumps?
It is swelling of the salivary glands after iodinated contrast dye, usually appearing within hours to a day after exposure.
Is it dangerous?
It is usually mild and resolves within days, but in this case the swelling became severe enough to require a breathing tube for three days.
Does it only affect people with kidney disease?
No. Only 39% of patients in a 2020 analysis had elevated creatinine, and this patient's kidney function was normal.
Is it an allergy?
It is generally attributed to iodine buildup in the glands, but this patient's skin test was positive for the specific dye used, suggesting an immune component in this case.
Can people who had it receive contrast again?
Possibly. Testing pointed to a different contrast agent as a safer option for this patient, though the report does not describe her receiving it. Decisions should be made with a clinician or allergist.
What should someone do if their glands swell after a scan?
Contact a clinician. Seek emergency care for any difficulty breathing or swallowing.
Published by Medicaldaily.com
