[Primary Nocardia asteroides deltoid abscess in treated Horton disease]

In a patient treated with high doses of corticosteroids for giant cell arteritis, a renewed rise in sedimentation rate accompanied by painful limitation of mobility of the shoulder led to the discovery of an intra-deltoid fluid collection. Aspiration yielded pus, culture showing the presence of Nocardia asteroides (NA). No portal of entry nor extramuscular sites of infection were found, justifying a diagnosis of primary nocardial muscle abscess. To the best of our knowledge, this is the first reported case. The opportunity is taken to review the epidemiological and clinical characteristics of NA infections as well as new management approaches.