Nocardia species have been called “great imitators” because of their variety of clinical presentations [22]. Nocardia is a well-known mimicker of several conditions of brain involvement, including primary brain tumor, metastases, and ischemic stroke [8, 23,24,25]. Nocardiosis is most commonly an opportunistic infection that causes both localized and systemic infections in the immunocompromised population. Brain involvement is rare, with N. cyriacigeorgica accounting for 2% of all brain abscesses [26]. A Nocardial brain abscess is 2.5 times more common among men [3]. The mortality rate of a Nocardia brain abscess is greater than 50%, which is three times higher than that of other bacterial causes of cerebral abscesses [10]. A Nocardial brain abscess is rare among the immunocompetent population. Publications consist solely of case reports involving one to three patients, and all of them were caused by species other than N. cyriacigeorgica, including N. farcinica, N. otitidiscaviarum, N. brasiliensis and N. abscessus [10,11,12,13,14,15,16, 27].
N. cyriacigeorgica was first isolated in 2001 by Yasin et al. from a patient with chronic bronchitis [17]. It has since been isolated from different clinical specimens and with a vast geographical distribution, including the USA, western Europe, Greece, Turkey, Japan, Thailand, and Canada [1]. A few case reports have described N. cyriacigeorgica brain abscess in immunocompromised patients [6,7,8, 17, 18, 28]. The main immunocompromised states that cause predisposition to brain abscesses are AIDS infection and diabetes mellitus [3]. Infections from N. cyriacigeorgica among immunocompetent patients are rare, and our search of the literature yielded case reports limited only to non-central nervous system infections [9].
It is well known that glucocorticoids have dose-dependent inhibitory effects on a broad range of immune system functions [19]. These inhibitory affects probably start at a low dose of glucocorticoid use [19]. However, the effects on phagocytic cell function with long-term, low-dose use are usually minimal [19]. The dose required to induce an increased risk of serious infections is a matter of controversy, with some studies claiming that a low dose of corticosteroids confers an increased risk while other studies argue that an increased risk occurs only with higher doses [20]. While the immunocompromising effects of the low dose prednisone were unknown in our patient, the fact that he was on long-term, low dose steroids, certainly possesses an important risk factor.
Nocardia species, as an opportunistic source of infection, commonly manifest in immunocompromised hosts, specifically in patients with conditions that impair T cell-mediated immunity [21]. These patients commonly receive prolonged regimens of glucocorticoids in addition to other immunosuppressant drugs or have other underlying immunosuppressive conditions [19].
The clinical course of Nocardiosis can be misleading, which was reflected in the current case whose presentation was initially thought to be an ischemic stroke and later determined as being a cerebral lesion. It can sometimes be difficult to recognize the source of symptoms as being an abscess at presentation, and a high clinical suspicion is needed. Frequent skin injuries incurred during gardening were a likely source of Nocardia inoculation, and, in retrospect, together with his long-term prednisone consumption history, were an important diagnostic clue in our patient.
In conclusion, Nocardia species are rare causes of brain abscess in immunocompetent patients. Their clinical presentation can mimic other, more common cerebral diseases. We report a case of a brain abscess caused by N. cyriacigeorgica in an immunocompetent patient that was thought to be an ischemic stroke at presentation and a space-occupying lesion later on. We believe that frequent skin injuries during gardening were a likely source of his Nocardia inoculation.