MedDRA preferred term · PML, a rare brain infection

Progressive multifocal leukoencephalopathy: adverse event reports recording this term

8,138 reports to FDA record it, 2004–2026; 0% of the database.

Read first · FDA's statement on these data

Adverse event reports submitted to FDA do not undergo extensive validation or verification. Therefore, a causal relationship cannot be established between product and reactions listed in a report. While a suspected relationship may exist, it is not medically validated and should not be the sole source of information for clinical decision making or other assumptions about the safety or efficacy of a product. Additionally, it is important to remember that adverse event reports represent a small percentage of total usage numbers of a product. Common products may have a higher number of adverse events due to the higher total number of people using the product. openFDA, FDA

FDA adds: "There is no certainty that the reported event (adverse event or medication error) was actually due to the product. FDA does not require that a causal relationship between a product and event be proven, and reports do not always contain enough detail to properly evaluate an event." The information in these reports "cannot be used to estimate the incidence of these events."

Do not rely on openFDA to make decisions regarding medical care. While we make every effort to ensure that data is accurate, you should assume all results are unvalidated.

Not medical advice. This site counts what was reported to FDA. Questions about a medicine or device belong with a pharmacist or clinician.

8,138
reports recording the term: 0% of all reports; 450
reports, 12 months to June 2026: 435 in the 12 months before; 99.5%
marked serious by the reporter: 57.4% across all reports; 32.4%
record death among outcomes, as reported: 9.1% across all reports

8,138 reports in FDA's adverse event database record the MedDRA term "Progressive multifocal leukoencephalopathy" (in plain words, PML, a rare brain infection): 0% of all reports received between January 2004 and June 2026. Coders pick the term that best matches the reporter's description.

450 reports recorded it in the 12 months to June 2026, close to the 435 of the 12 months before. FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases. Of reports recording this term, 99.5% are marked serious, 32.4% include death among the outcomes and 49.6% include hospitalisation, as reported.

The drugs listed most often as suspect products in those reports are Tysabri, Rituximab and Cyclophosphamide. That order mostly follows how many reports each drug has overall; the table also gives the term's share within each drug's own reports. FDA states that "a causal relationship cannot be established between product and reactions listed in a report" and that for any given report "there is no certainty that a suspected drug caused the event."

Reports by month, five years

FDA releases FAERS data quarterly, so the newest months are incomplete and grow in later releases.

Drugs listed as suspect products in these reports

Drug	Class	Reports with this term	Share of the drug's own reports
Tysabri	Integrin receptor antagonist	2,048	1.2%
Rituximab	CD20-directed cytolytic antibody	1,445	0.9%
Cyclophosphamide	Alkylating drug	974	0.7%
Prednisone	Corticosteroid	739	0.4%
Mabthera	—	537	2.5%
Prednisolone	Corticosteroid	526	0.6%
Mycophenolate mofetil	Antimetabolite immunosuppressant	475	0.6%
Methotrexate	Folate analog metabolic inhibitor	464	0.2%
Tacrolimus	Calcineurin inhibitor immunosuppressant	452	0.5%
Rituxan	CD20-directed cytolytic antibody	399	1%
Vincristine	—	351	0.6%
Dexamethasone	Corticosteroid	322	0.2%
Doxorubicin	Anthracycline topoisomerase inhibitor	299	0.5%
Fludarabine	Nucleoside metabolic inhibitor	271	1.3%
Azathioprine	Purine antimetabolite	267	0.8%
Methylprednisolone	Corticosteroid	249	0.5%
Bendamustine	—	242	2%
Etoposide	Topoisomerase inhibitor	237	0.4%
Gilenya	Sphingosine 1-phosphate receptor modulator	209	0.3%
Cyclosporine	Calcineurin inhibitor immunosuppressant	193	0.5%
Doxorubicin hydrochloride	Anthracycline topoisomerase inhibitor	179	0.5%
Cytarabine	Nucleoside metabolic inhibitor	174	0.3%
Lenalidomide	Thalidomide analog	147	0.2%
Melphalan	Alkylating drug	143	0.8%
Cisplatin	Platinum-based drug	139	0.2%

Drugs with a page on this site, ordered by the number of their reports recording this term. The last column is the term's share within that drug's own reports, against 0% across the whole database. FDA states that adverse event reports "represent a small percentage of total usage numbers of a product", that "common products may have a higher number of adverse events due to the higher total number of people using the product", and that the data "by themselves are not an indicator of the safety profile of the drug or biologic."

By pharmacologic class

Class	Reports with this term	Share of class reports	Median drug in class
Integrin receptor antagonist	2,143	0.8%	0.7%
CD20-directed cytolytic antibody	2,064	0.7%	0.3%
Corticosteroid	1,909	0.2%	0%
Alkylating drug	1,602	0.6%	0.1%
Nucleoside metabolic inhibitor	713	0.2%	0.1%
Calcineurin inhibitor immunosuppressant	699	0.3%	0%
Antimetabolite immunosuppressant	664	0.5%	0.6%
Folate analog metabolic inhibitor	541	0.2%	0%
Anthracycline topoisomerase inhibitor	500	0.5%	0.1%
Thalidomide analog	352	0.1%	0.1%

Classes ordered by count. Class shares follow the class's overall report volume as much as anything else.

Patients in these reports

Patient age

Under 20%4

2 to 110.5%42

12 to 170.7%61

18 to 4419.3%1,568

45 to 6434.7%2,824

65 to 7414.3%1,160

75 and over7.6%616

Age not given22.9%1,863

Patient sex

Female50.8%4,134

Male38.6%3,140

Not given10.6%864

Grey bar: all 20,646,523 reports in the database. 27.8% of these reports give the United States as the country.

Questions about "Progressive multifocal leukoencephalopathy"

What does "Progressive multifocal leukoencephalopathy" mean in an adverse event report?

In plain language: PML, a rare brain infection. It is a MedDRA preferred term, the dictionary FDA uses to code what a reporter described. The report's own description is not published by openFDA and is not shown here.

How many reports record progressive multifocal leukoencephalopathy?

8,138 reports through June 2026 (0% of all reports), 450 of them in the latest 12 months.

Which drugs appear most often in these reports?

Tysabri (2,048), Rituximab (1,445), Cyclophosphamide (974), Prednisone (739) and Mabthera (537). Drugs with many reports overall lead almost every term's list. FDA states that adverse event reports "represent a small percentage of total usage numbers of a product", that "common products may have a higher number of adverse events due to the higher total number of people using the product", and that the data "by themselves are not an indicator of the safety profile of the drug or biologic."

Does a drug appearing here mean it was responsible for this reaction?

No. FDA states that "a causal relationship cannot be established between product and reactions listed in a report" and that for any given report "there is no certainty that a suspected drug caused the event."

I have this symptom. What should I do?

This site cannot assess anyone. A pharmacist or clinician can; for an emergency, call the local emergency number. Nothing on this page is medical advice.

Where this comes from. Counts are built from the openFDA Drug Adverse Event (FAERS) bulk export released 28 Sep 2026, which holds reports FDA received through 30 Jun 2026. Drug names are as reported, resolved to the brand or generic name on the FDA label where openFDA's harmonisation matched them; classes are the pharmacologic class (EPC) from the label and the National Drug Code Directory of 17 Sep 2026. Terms are pooled across spelling and capitalisation variants of one MedDRA preferred term. No report narrative, lot number, patient detail or reporter identity is published. See the methodology and sources; FDA's record is authoritative, and corrections are handled within five working days.

Drug data (FAERS) through 30 Jun 2026; device data (MAUDE) through 31 Aug 2026. Not medical advice.