Background Aromatase inhibitors (AI) are used in postmenopausal women for adjuvant treatment of hormone receptor positive breast cancer. AI led to profound oestrogen suppression and may be expected to increase the risk of carpal tunnel syndrome (CTS).

Purpose To determine the strength of the association between pharmaceutical products containing AI (anastrozole, letrozole and exemestane) and the occurrence of CTS.

Material and methods For this purpose, we used a case/non-case approach in the WHO Global Individual Case Safety Report database (VigiBase). This database is available from Uppsala Monitoring Centre and contains national data from over 100 countries and case reports dating back to 1968. WHO have implemented the information component (IC) as point estimates of association; an IC above 0 is considered an association.

Cases were defined as reports of CTS; non-cases were defined as reports of all reactions other than CTS. Exposure was defined as the mention of AI in a report, either being or not being suspected of causing the reaction.

The association between AI and CTS was estimated by means of the reported odds ratio (ROR); a lower limit of the 95% confidence interval of the ROR above 1 is considered as a potential signal.

Results The total number of cases included in this database so far is 10 619 032 (March 2015), 4516 corresponding to cases of CTS, and 5.3% associated with AI.

The overall ROR were: anastrozole 35.5 (30.1–41.9), letrozole 10.6 (7.6–14.7) and exemestane 39.2 (30.1–51.1). Most cases were in women (97%), and a 46% in 45–64-year-old patients.

Conclusion AI is associated with CTS; the association is higher in women and in those aged 45–64 years. As this association has already been described, the present study further emphasised the important of this association. Information from spontaneous reporting confirms the association observed in a clinical trial.

No conflict of interest.