Magnetic resonance imaging and magnetic resonance spectroscopy in Salmonella meningoencephalitis.

Dear Sir,

Salmonella meningitis is a rare form of bacterial meningitis but remains a threat in children below 2 years of age.[1] The first case of Salmonella meningitis was described by Ghon in 1907.[2] Magnetic resonance imaging (MRI) findings in Salmonella meningoencephalitis is sparsely described. We report a case of a 5-month-old infant with meningoencephalitis on MRI caused by Salmonella species.

A 5-month-old infant was admitted to the Pediatric Intensive Care Unit (ICU) with 3 days history of high-grade fever and one episode of focal seizures involving the left arm. On examination, the infant was febrile (temperature - 102°F), had a Glasgow Coma Scale of 11/15 and exaggerated deep tendon reflexes. Laboratory studies revealed a total leukocyte count of 13,030/cu.mm with 69% polymorphs and 22% lymphocytes. As the patient did not respond to routine anticonvulsants, she was started on levetiracetam and midazolam infusion following which the frequency of seizures reduced. Lumbar puncture was done, and cerebrospinal fluid (CSF) sent for analysis along with blood and urine culture. CSF showed a leukocyte count of 4540/cu.mm with 76% polymorphs and 24% lymphocytes. CSF glucose and proteins were 44 mg/100 ml and 227 mg/100 ml, respectively. Gram stain of CSF revealed plenty of inflammatory cells and Gram-negative bacilli. Based on the CSF report, a diagnosis of pyogenic meningitis was made, and the patient was started on meropenem and vancomycin.

On the 3rd day of admission, the patient was referred for MRI of the brain. The study revealed white matter signal abnormalities and multiple lesions of size 1–3 mm with restricted diffusion in bilateral corona radiata region [Figure 1a–c]. Following contrast administration, these lesions showed peripheral enhancement [Figure 1d–f]. Diffuse cerebral meningeal enhancement was also noted [Figure 1f]. Magnetic resonance (MR) spectroscopy with intermediate TE (144 ms) showed increased choline reduced N-acetyl aspartate (NAA) with choline/NAA ratio of 2.41. Small lipid lactate peak confirmed these tiny focal lesions as representing microabscesses [Figure 2]. MR spectroscopy with short TE (35 ms) was then attempted hoping to see some specific peaks. Unfortunately, as the child was coming out of sedation proper spectrum could not be obtained. Further sedation could not be administered as the child was very sick to take further sedation. Based on the above features, a radiological diagnosis of meningoencephalitis with multiple microabscesses was made. The blood and CSF cultures were positive for Gram-negative bacilli, identified as Salmonella species, which were sensitive to ampicillin, cefepime, ceftriaxone, meropenem, levofloxacin, and cefepime. Subsequently, the patient was administered ceftriaxone and ampicillin for 21 days. Following this treatment, the patient's condition improved and she became asymptomatic.

Figure 1

(a) Axial T2-weighted image showing small hyperintense lesions (black arrows) in bilateral centrum semiovale. (b and c) Axial diffusion-weighted images showing restricted diffusion of these lesions (open arrows). (d and e) Postcontrast axial T1-weighted images show patchy and peripherally enhancing lesions in bilateral corona radiata and centrum semiovale (arrowhead). (f) Postcontrast coronal T1-weighted image shows diffuse meningeal enhancement (white arrow)

Figure 2

Magnetic resonance spectroscopy (TE-144 ms) with voxel within the lesion shows elevated choline, decreased N-acetyl aspartate with Cho/N-acetyl aspartate ratio of 2.41 and a small lipid lactate peak

The most common serotypes of Salmonella causing meningitis are Salmonella typhimurium, Salmonella typhi, Salmonella enteritidis, and S. Habana. Salmonella meningitis is rare and is primarily a disease of the infants due to the increased permeability of the blood–brain barrier.[3] The prognosis and course of Salmonella meningoencephalitis differ significantly from other causes of meningitis and carries a high morbidity of 50–90%. Molyneux et al. reported a mortality rate of 58% with the development of neurological sequelae in 8% of 61 Salmonella meningitis cases.[4]

MRI findings described include normal MRI brain, diffuse cerebral vasogenic edema, edema of splenium, and focal white matter edema associated with cerebritis.[5] Salmonella meningoencephalitis is associated with a high incidence of acute neurological complications such as subdural effusion/empyema, abscesses, ventriculitis, cerebritis, hydrocephalus, venous thrombosis, and infarcts.[6] Advanced MRI offers a noninvasive means of detecting these neurological complications. MRI study in our case although nonspecific revealed complications such as cerebritis and microabscesses which can be seen in any other purulent intracranial infection. MR Spectroscopy played a complementary role as the presence of elevated lipid lactate peak helped in confirming the presence of microabscesses within areas of cerebritis.

Medical management with III generation cephalosporins and fluoroquinolones had a high cure rate (>80%) and reduced the mortality by 10%.[7] Patient should be monitored in the ICU in case of seizures or any other severe complications. Surgical drainage is required in cases of subdural empyema/effusion. In conclusion, Salmonella encephalopathy is a distinctive clinical entity and requires MRI and laboratory investigations are needed for early detection of complications and for appropriate management.

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Conflicts of interest

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