Nocardiosis is a rare infection caused by bacteria of the genus Nocardia spp. It primarily affects immunocompromised individuals, such as solid organ or hematopoietic stem cell transplant recipients, as well as individuals with anti-GM-CSF antibodies. The infection typically begins by inhalation, affecting the lungs, with frequent hematogenous spread to the brain and soft tissues. Cerebral involvement is present in 20 to 40% of cases, although 40% of patients remain neurologically asymptomatic.

Treatment consists of prolonged antibiotic therapy and, sometimes, surgical drainage for large or refractory abscesses. Mortality associated with cerebral involvement varies between 20 and 40%. Although radiological improvements are observed under treatment, the link between image changes and clinical prognosis remains uncertain. Regular radiological monitoring is recommended during and after treatment, although the expected evolution has not been described in the literature.

Nocardiosis is a rare infection caused by bacteria of the genus Nocardia spp. It primarily affects immunocompromised individuals, such as solid organ or hematopoietic stem cell transplant recipients, as well as individuals with anti-GM-CSF antibodies. The infection typically begins by inhalation, affecting the lungs, with frequent hematogenous spread to the brain and soft tissues. Cerebral involvement is present in 20 to 40% of cases, although 40% of patients remain neurologically asymptomatic. Brain imaging is essential for diagnosis, with MRI often being preferred due to its sensitivity. Images often show multiple abscesses, but without sufficient specificity to differentiate nocardiosis from other pathogens. New MRI techniques could improve lesion characterization.

Treatment consists of prolonged antibiotic therapy and, sometimes, surgical drainage for large or refractory abscesses. Mortality associated with cerebral involvement varies between 20 and 40%. Although radiological improvements are observed under treatment, the link between image changes and clinical prognosis remains uncertain. Regular radiological monitoring is recommended during and after treatment, although the expected evolution has not been described in the literature.

Inclusion Criteria:

• Minor or adult patient with cerebral nocardiosis, defined by the presence of compatible clinical and radiological signs associated with the detection of Nocardia spp. in a biological sample (cerebral or extracerebral).

• With available imaging tests:

  • All patients with 3 brain imaging tests at the 3 stages of treatment: within 2 weeks of diagnosis, upon transition to maintenance treatment (3-6 weeks after the start of treatment), and at the end of treatment (between 1 month before and 1 month after the end of antibiotic treatment). MRI scans are preferred; in the absence of MRI images, contrast-enhanced CT scans will be included.
  • OR: any patient who has undergone an MRI and a contrast-enhanced CT scan within two weeks of diagnosis, with the two tests performed within 72 hours of each other.
  • OR: any patient with a multimodal brain MRI at any time during infection, preferably within one month of diagnosis.

Exclusion Criteria:

• Refusal or impossibility of information.

Patient with cerebral nocardiosis and cared at an Assistance Publique -Hôpitaux de Paris hospital between 01/01/2004 and 01/12/2024.