Cat-scratch disease encephalitis

Clinical History

An 8-year-old boy presented to the ER with a tonic-clonic convulsive status which started while playing videogames. Previous relevant medical history included a chronic suppurative otitis and a clinically suspected muscular fibrillar rupture in the right inguinal area.

Imaging Findings

An unenhanced brain CT was obtained and considered normal (Fig. 1)

After careful physical evaluation, an erythematous lump in the right inguinal area was found which was not consistent with a fibrillar rupture. Sonography revealed a hypoechoic rounded lesion with vascular hilum closely related to a subcutaneous collection (with fluid drainage to the skin), compatible with suppurative inflammatory lymphadenopathy (Fig. 2).

Additionally, abdominal US revealed multiple hypoechoic and rounded small lesions (<1cm) affecting liver and spleen (Fig. 3, 4, 7).

Due to persistent encephalopathic behaviour, a brain and liver MRI was performed. Brain MRI showed signal abnormality on DWI in multiple cortical areas without restricted diffusion on the ADC. This would be in keeping with focal areas of cerebral oedema. (Fig. 5). Liver MRI confirmed the presence of multiple T2-hyperintense lesions showing restricted diffusion, compatible with granulomas/micro-abscesses (Fig. 6).

Discussion

BACKGROUND
Cat-scratch disease (CSD) is an infection caused by Bartonella henselae. It usually affects children and young adults, and 87% of cases occur in those younger than 18 years of age. Cats are the principal reservoir. Infection is transmitted by a cat scratch or bite, and spreads through the lymphatic system [1].

CLINICAL PERSPECTIVE
After inoculation, cutaneous lesions may appear 3-10 days later and progress from erythematous to papular, and finally crusted stages. Single regional lymphadenopathy could typically appear (axillary, epitrochlear, head/neck, groin). Suppurative nodes require drainage in 10% of cases. A low-grade fever might be present. Rarely, dissemination to various organs may occur, most often liver, spleen, and bone marrow (hepatosplenic dissemination, vertebral osteomyelitis). Spread occurs less frequently to the CNS (Parinaud syndrome, neuroretinitis, encephalitis/encephalopathy). Encephalitis is characterised by headaches, nuchal rigidity, and mental status changes [1, 2, 5].

IMAGING PERSPECTIVE
Lymphadenopathy: US may show enlarged, sometimes hyperaemic lymph nodes with or without central necrosis, and approximately 10% will suppurate and require drainage.

Hepatosplenic lesions: Multiple lesions of variable size/shape throughout the liver or spleen, compatible with granulomas/microabscesses. On US and CT, lesions are usually hypoechoic and hypoattenuating. After contrast administration, hepatosplenic granulomas may show variable peripheral enhancement. Healed lesions may show calcifications [3, 4, 5, 6].

Encephalitis: Cat-scratch-related encephalitis/meningitis show T2 and FLAIR hyperintensity in various regions of the brain. Post contrast-enhanced T1-weighted images may reveal focal or diffuse leptomeningeal enhancement. In our case, signal abnormality on the DWI in multiple cortical areas without restricted diffusion on the ADC was observed, in keeping with focal areas of cerebral oedema (Fig.5) [7, 8, 9, 10, 11].

OUTCOME
Detection of B. henselae is accomplished by serology studies which have replaced biopsy. If biopsy is performed, it shows granulomata with central necrosis and microabscesses. In our case, a serologic test and a biopsy were performed, confirming the presence of Bartonella henselae in both.

Most patients have self-limited lymphadenopathy and do not require antibiotics. CSD disseminated to the liver, spleen, eye, or central nervous system may require antibiotics, as was the case with our patient. Use of oral azithromycin for mild to moderate disease or a combination of erythromycin or doxycycline plus rifampin for encephalitis/meningitis may be effective. [1]

Most patients recover fully although a small percentage may develop complications [7].

TAKE HOME MESSAGE

- Infection starts after a scratch or bite from a cat/kitten.

- After inoculation, cutaneous lesions may appear in association with regional lymphadenopathy (axillary, epitrochlear, head/neck, groin).

- Rarely, dissemination to various organs occurs, most often liver, spleen, bone marrow.

- Encephalitis is a rare complication (2-4%).

- Most patients make a full recovery.

Differential Diagnosis List

Final Diagnosis

Cat-scratch disease encephalitis

URL:	https://www.eurorad.org/case/13381
DOI:	10.1594/EURORAD/CASE.13381
ISSN:	1563-4086