Cat at home? Cat scratch disease with atypical presentations and aggressive radiological findings mimicking sarcoma, a potential diagnostic pitfall

Abstract

Background and purpose - Cat scratch disease (CSD) is a self-limiting disease caused by Bartonella (B.) henselae. It is characterized by granulomatous infection, most frequently involving lymph nodes. However, it can present with atypical symptoms including musculoskeletal manifestations, posing a diagnostic challenge. We describe the prevalence and demographics of CSD cases referred to a sarcoma center, and describe the radiological, histological, and molecular findings.Patients and methods - Our cohort comprised 10 patients, median age 27 years (12-74) with clinical and radiological findings suspicious of sarcoma.Results - 7 cases involved the upper extremities, and 1 case each involved the axilla, groin, and knee. B. henselae was found in 6 cases tested using polymerase chain reaction and serology in 5 cases. 9 cases were soft tissue lesions and 1 lesion involved the bone. 1 patient had concomitant CSD with melanoma metastasis in enlarged axillary lymph nodes. On MRI, 5 soft tissue lesions were categorized as probably inflammatory. In 3 cases, with still detectable lymph node structure and absent or initial liquefaction, the differential diagnosis included lymph node metastasis. A sarcoma diagnosis was suggested in 4 cases. The MRI imaging features of the bone lesion were suspicious of a bone tumor or osteomyelitis.Interpretation - Atypical imaging findings cause a diagnostic challenge and the differential diagnosis includes malignant neoplasms (such as sarcoma or carcinoma metastasis) and other infections. The distinction between these possibilities is crucial for treatment and prognosis.

Figure 1.

Diagram depicting the patient population and the reasons for inclusion in our cohort.

Figure 2.

Case no. 10. A 37-year-old female with an infrapatellar infiltrative soft tissue lesion of the knee. (A) Proton density (PD) image shows irregular heterogeneous soft tissue lesion in subcutaneous tissue just anterior to patellar ligament with surrounding edema (white arrow) and joint effusion. (B) Homogenous hypointense signal intensity on T1-weighted image (white arrow). (C) Axial PD image shows the hyperintense lesion and extension of soft tissue edema (white arrow). (D) Sagittal T1 VIBE image after application of Gd-contrast shows homogenous contrast enhancement of the lesion with an irregular margin (white arrow). On all sequences, the patellar ligament is intact. (E–F) Histology shows fatty tissue with extensive fibrosis and numerous granulomas with central necrosis. (G–H) Central necrosis (black stars) is often stellate in appearance with admixed neutrophils and surrounded by palisading histiocytes (black arrows, H).

Figure 2.

Case no. 10. A 37-year-old female with an infrapatellar infiltrative soft tissue lesion of the knee. (A) Proton density (PD) image shows irregular heterogeneous soft tissue lesion in subcutaneous tissue just anterior to patellar ligament with surrounding edema (white arrow) and joint effusion. (B) Homogenous hypointense signal intensity on T1-weighted image (white arrow). (C) Axial PD image shows the hyperintense lesion and extension of soft tissue edema (white arrow). (D) Sagittal T1 VIBE image after application of Gd-contrast shows homogenous contrast enhancement of the lesion with an irregular margin (white arrow). On all sequences, the patellar ligament is intact. (E–F) Histology shows fatty tissue with extensive fibrosis and numerous granulomas with central necrosis. (G–H) Central necrosis (black stars) is often stellate in appearance with admixed neutrophils and surrounded by palisading histiocytes (black arrows, H).

Figure 3.

Case no. 7. A 40-year-old female with an epifascial soft tissue lesion of the upper arm. (A) On a T1-weighted image, the lesion with intermediate signal intensity and irregular margin; wide contact with the underlying fascia (arrow). (B) Homogenous high T2-weighted signal intensity without any surrounding edema (arrow). (C) Coronal T1-weighted image with fat saturation after application of Gd-contrast shows heterogeneous contrast enhancement (arrow). (D–E) DWI image (D) with corresponding (E) ADC map shows diffusion restriction due to necrotic collection (circles).

Figure 4.

Case no. 5. A 13-year-old female with osteomyelitis of distal humerus as a late manifestation of cat scratch disease. (A) AP radiography of the elbow with discrete permeative osteodestruction pattern, cortical irregularity, and no periosteal reaction (circle). (B–C) Bone marrow infiltration of the medial epicondyle with permeative destruction of underlying cortex on axial proton density image (arrow, B) and coronal T1-weighted (arrow, C). (D) Bone marrow edema in the area and extraosseous extension with cortex destruction. Abnormal thickening and increased T2-weighted signal intensity within the common flexor origin from the lateral epicondyle due to inflammatory infiltration (white arrow) with edema of the surrounding subcutaneous fat tissue. (E) Corresponding color Doppler sonography shows cortical discontinuity with extraosseous soft tissue extension without significant hypervascularisation of the surrounding structures (yellow star).

Figure 4.

Case no. 5. A 13-year-old female with osteomyelitis of distal humerus as a late manifestation of cat scratch disease. (A) AP radiography of the elbow with discrete permeative osteodestruction pattern, cortical irregularity, and no periosteal reaction (circle). (B–C) Bone marrow infiltration of the medial epicondyle with permeative destruction of underlying cortex on axial proton density image (arrow, B) and coronal T1-weighted (arrow, C). (D) Bone marrow edema in the area and extraosseous extension with cortex destruction. Abnormal thickening and increased T2-weighted signal intensity within the common flexor origin from the lateral epicondyle due to inflammatory infiltration (white arrow) with edema of the surrounding subcutaneous fat tissue. (E) Corresponding color Doppler sonography shows cortical discontinuity with extraosseous soft tissue extension without significant hypervascularisation of the surrounding structures (yellow star).

Figure 5.

Case no. 9. A 74-year-old male with lymph node melanoma metastasis and synchronous cat scratch disease. (A) Enlarged axillary lymph nodes with heterogenous contrast enhancement on coronal postcontrast T1-weighted image with fat saturation; no signs of necrosis (star). (B) Sonography shows irregular 28 x 26 mm large lymph nodes with the heterogeneous structure without necrosis and hyperechogenic surrounding subcutaneous tissue (arrow). (C) On axial short tau inversion recovery (STIR) image and (D) T1-weighted image pathologically changed lymph nodes with a heterogenous signal. Centrally, on T2-weighted image low signal intensity with hyperintense signal intensity on T1-weighted image corresponds to melanin (arrows). (E) Histologically shows granuloma with central necrosis (star) and malignant melanoma metastasis (arrow). (F) Higher-power view of the granuloma with extensive central necrosis, surrounded by palisading histiocytes and (G) atypical melanocytes. (H) Malignant melanoma is immunohistochemically positive with SOX10 (Inlet: positive reaction to Melan A).

Figure 5.

Case no. 9. A 74-year-old male with lymph node melanoma metastasis and synchronous cat scratch disease. (A) Enlarged axillary lymph nodes with heterogenous contrast enhancement on coronal postcontrast T1-weighted image with fat saturation; no signs of necrosis (star). (B) Sonography shows irregular 28 x 26 mm large lymph nodes with the heterogeneous structure without necrosis and hyperechogenic surrounding subcutaneous tissue (arrow). (C) On axial short tau inversion recovery (STIR) image and (D) T1-weighted image pathologically changed lymph nodes with a heterogenous signal. Centrally, on T2-weighted image low signal intensity with hyperintense signal intensity on T1-weighted image corresponds to melanin (arrows). (E) Histologically shows granuloma with central necrosis (star) and malignant melanoma metastasis (arrow). (F) Higher-power view of the granuloma with extensive central necrosis, surrounded by palisading histiocytes and (G) atypical melanocytes. (H) Malignant melanoma is immunohistochemically positive with SOX10 (Inlet: positive reaction to Melan A).