Abstract
Case summary
A 7-year-old female spayed domestic shorthair cat presented with respiratory distress. Initial diagnostics revealed a large cystic mass in the mediastinum and moderate hyperglobulinaemia. Additional abnormalities were ruled out through thoracic and abdominal CT. The mass was surgically removed, and antibiotic treatment was started based on cytological findings of intralesional bacteria. Histopathology and microbiology confirmed a severe inflammatory reaction pattern compatible with feline eosinophilic sclerosing fibroplasia (FESF) associated with Staphylococcus aureus. After surgery and antibiotic therapy, clinical signs and related abnormalities fully resolved. At the time of writing, 24 months postoperatively, the patient shows no evidence of relapse.
Relevance and novel information
FESF, initially described as an inflammatory condition affecting the gastrointestinal tract, has also been anecdotally reported in other locations, including the retroperitoneum, retropharyngeal region and mediastinum. This report is the second to document a mediastinal presentation without concurrent abdominal involvement, and the first to achieve long-term remission without the use of immunosuppressants. It supports the hypothesis that FESF may represent a characteristic pattern of inflammation secondary to a range of triggers rather than a distinct disease process, indicating that treatment should probably target the specific underlying cause.
Introduction
Feline eosinophilic sclerosing fibroplasia (FESF) is a distinctive inflammatory response in cats, characterised histologically by dense collagen trabeculae, fibroblasts and eosinophils. The condition, of uncertain aetiology, was initially reported in the gastrointestinal tract and regional lymph nodes as feline gastrointestinal eosinophilic sclerosing fibroplasia (FGESF).1,2 Recent case reports have documented FESF in non-gastrointestinal locations,3 –5 including areas outside the abdominal cavity.6 –8 Two case reports have described FESF in mediastinal lymph nodes secondary to primary abdominal disease.2,7 More recently, FESF has been reported for the first time as a solitary primary intrathoracic mass in a cat without apparent gastrointestinal involvement at the time of diagnosis. However, the cat died a few weeks later with gastrointestinal signs and a post-mortem examination was not performed. 8
This report details a rare case of FESF presenting as a mediastinal mass with no gastrointestinal disease. Surgical resection and antibiotic therapy led to complete resolution, without the use of immunosuppressants, and the cat has remained disease-free for at least 24 months at the time of writing.
Case description
A 7-year-old female spayed domestic shorthair cat was referred for evaluation of a 3-week history of progressive tachypnoea, lethargy and hyporexia. The cat, which had outdoor access, had not received routine vaccinations or deworming, and tested negative for feline leukaemia and immunodeficiency viruses (SNAP test; Idexx). The initial veterinary evaluation detected a thoracic mass on thoracic ultrasound, prompting referral for further investigation.
On presentation, physical examination showed tachypnoea with no other notable findings. Complete blood count results were within normal limits (Table 1); however, serum biochemistry revealed elevated total protein (9.6 g/dl, reference interval [RI] 5.4–8.2), hyperglobulinaemia (6.5 g/dl, RI 1.5–5.7) and total hypercalcaemia (13.8 mg/dl, RI 8–11.8) (Table 2). Echocardiography and abdominal ultrasound showed no abnormalities.
Haematological findings in a cat with mediastinal feline eosinophilic sclerosing fibroplasia at the time of presentation
Serum biochemical findings in a cat with mediastinal feline eosinophilic sclerosing fibroplasia at the time of presentation and 20 days postoperatively
Bold values indicate results outside the reference interval.
Thoracic and abdominal CT revealed a large cystic mass in the cranial mediastinum, causing dorsal displacement of the trachea and lateral displacement of the heart (Figure 1a,b). Ultrasound-guided fine-needle aspiration showed a mixed inflammatory response and necrosis, with both intra- and extracellular coccoid bacteria present.
(a) Sagittal and (b) transverse images, obtained by CT with contrast, demonstrating the presence of a large mediastinal cystic mass, displacing the heart and lungs caudally and to the right
A caudal exploratory sternotomy was performed, revealing an encapsulated mass in the cranial mediastinum (Figure 2). The mass was resected using an electrosurgical scalpel, and a thoracic drain and oesophagostomy tube were placed. Tissue samples were sent for microbiological culture and histopathological examination. Postoperative treatment included antibiotic treatment (amoxicillin-clavulanic acid 20 mg/kg q8h and marbofloxacin 5 mg/kg q24h), methadone (0.2 mg/kg q4h), meloxicam (0.05 mg/kg q24h) and maropitant (1 mg/kg q24h). The thoracic drain was removed 2 days postoperatively and the cat was discharged 3 days postoperatively with a normalised respiratory rate. Medication was continued at home, switching methadone for tramadol (4 mg/kg q8–12h).
Mediastinal encapsulated mass observed and removed during an exploratory sternotomy
Ten days postoperatively, the owner reported an improvement in the cat’s breathing and demeanour, although its appetite had not yet normalised. At this point, no further tests were conducted at the owner’s request.
Histopathological analysis revealed streams of poorly cellular collagenous tissue arranged in thick, anastomosing trabeculae, interspersed with frequent plasma cells, lymphocytes and lower numbers of eosinophils. There were central areas of necrosis (possibly the cystic areas seen on CT scan), with neutrophils, mineralisation and abundant macrophages with occasional multinucleated giant cells with randomly located nuclei (foreign-body type cells). Gram-positive coccoid bacteria were identified on Gram stain, while Ziehl-Neelsen staining was negative. This histological pattern was consistent with FESF (Figure 3a–d), with intralesional bacteria. The presence of lymph node-like lymphoid tissue at the periphery of the mass was suspicious of a mediastinal lymph node. Staphylococcus aureus was isolated and found to be sensitive to all antibiotics tested. Meloxicam, tramadol and marbofloxacin were discontinued, and the feeding tube was retained to facilitate the administration of amoxicillin-clavulanic.
(a–d) Haematoxylin and eosin-stained histopathological image of feline eosinophilic sclerosing fibroplasia showing trabecular collagenous deposition with areas of sclerosis and inflammatory infiltration, including eosinophils. Scale bar: 50 µm
At the 3-week postoperative recheck, the cat was clinically normal and had a good appetite. The previous clinicopathological abnormalities had resolved (Table 2). Abdominal ultrasound and thoracic radiographs were also unremarkable (Figure 4a,b). The oesophagostomy tube was removed and amoxicillin-clavulanic acid was discontinued. At the time of writing, 24 months after diagnosis, the cat remains asymptomatic and periodic thoracic and abdominal imaging remain unremarkable.
(a) Ventrodorsal and (b) right lateral radiograph recheck 17 days after surgical removal of mediastinal feline eosinophilic sclerosing fibroplasia
Discussion
FGESF, an inflammatory condition previously misidentified as neoplasia, is now acknowledged as a common differential diagnosis for gastrointestinal masses, often accompanied by lymphadenopathy.1,2 However, recent studies have documented similar histological patterns in locations beyond the gastrointestinal tract,3 –5 particularly in the lymph nodes, and even in areas outside the abdominal cavity.6 –8 As a result, a recent publication proposed adopting a more inclusive term, ‘feline eosinophilic sclerosing fibroplasia (FESF)’, to better reflect the broader spectrum of affected sites. 6 In the present case, the inflammation was mixed with only low numbers of eosinophils, but with abundant formation of collagenous trabeculae typical of FESF. Macrophages were present in areas of necrosis, where they may represent the phagocytosis of necrotic debris, although initial triggers such as foreign material or lymph cannot be excluded. This case, therefore, supports the adoption of the new nomenclature for a characteristic pattern of inflammation, encouraging clinicians to consider FESF as a differential diagnosis for masses outside the gastrointestinal tract.
While the precise pathogenesis of FESF remains unclear, microorganisms are hypothesised to play a role in many cases.1,2 Though bacteria are most frequently implicated,1 –3,6,8 –12 fungi have also been detected.11 –13 It is still uncertain whether these microorganisms act as primary risk factors or as secondary opportunistic infections resulting from gastrointestinal mucosal damage. However, given that the mediastinum is a typically sterile environment, the presence of microorganisms in this area is more likely to reflect a primary disease process.
Clinicopathological findings in FESF typically include mild to moderate eosinophilia in approximately 50% of cases,1,2,9,10 mild hypoalbuminaemia in 28–45%2,9 and hyperglobulinaemia in 14–64% of cases.2,9 No significant abnormalities in calcium levels have been reported; however, one recent study reported hypocalcaemia in 10% of patients, 67% of whom had normal albumin levels. 9 In the present case, neither eosinophilia nor hypoalbuminaemia were identified, although hyperglobulinaemia and total hypercalcaemia were noted at presentation, both of which resolved after treatment. Owing to financial constraints, ionised calcium levels were not assessed at diagnosis, leaving it unclear whether true hypercalcaemia was present. If confirmed, hypercalcaemia could be attributed to granulomatous inflammation in the lesion, a recognised cause of hypercalcaemia in cats. 14
Initial reports of FESF described clinical signs related to gastrointestinal disease;1,2,9 however, in more recent reports of non-gastrointestinal FESF, dyspnoea, pleural effusion, cough, sneezing and nasal discharge were also seen.2,6 –8 Based on the growing evidence of mediastinal FESF, this condition should be considered a differential diagnosis for clinical signs associated with mediastinal disease.
A multimodal approach, combining surgery with immunosuppressive and antimicrobial therapy, is generally recommended for cases of FGESF to reduce relapse and improve survival. 2 However, the optimal treatment strategy for each individual case remains unclear. Nearly all cases described in the literature have been treated with prednisolone2,9,10 or a combination of prednisolone and a second immunosuppressant,2,4 most commonly cyclosporine. No cases have been reported with favourable long-term outcomes without the use of immunosuppression. The role of antibiotics remains poorly defined, as many of the documented cases involved concurrent antibiotic administration. In a recent study of 60 cats with FGESF, 72% received antibiotics, but their use did not significantly affect survival. 9 This report describes a cat with FGESF that was treated using surgical resection and antibiotics alone, marking the first documented case with a favourable long-term outcome without the use of immunosuppressive therapy. As various triggers may contribute to the development of eosinophilic sclerosing fibroplasia, treatment strategies targeting the underlying aetiologies may need to be tailored to each individual patient. In this instance, dual antibiotic therapy was initiated pending culture results. For more rational antibiotic use, a single broad-spectrum antibiotic would have been preferable. Further research is needed to determine which cases require antibiotics and which drugs should be used empirically as first-line therapy pending culture results.
Conclusions
FESF can manifest in sites beyond the gastrointestinal tract, often in association with lymphoid tissue and without concurrent gastrointestinal or abdominal disease. These findings support a revised nomenclature that omits the term ‘gastrointestinal’. The presence of bacteria in FESF lesions highlights the importance of microbiological culture and microorganism identification, especially in non-gastrointestinal sites. In the present case, complete surgical resection combined with antibiotic therapy resolved the disease without the use of immunosuppressants, resulting in a long-term, relapse-free survival.
Footnotes
Conflict of interest
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
Ethical approval
The work described in this manuscript involved the use of non-experimental (owned or unowned) animals. Established internationally recognised high standards (‘best practice’) of veterinary clinical care for the individual patient were always followed and/or this work involved the use of cadavers. Ethical approval from a committee was therefore not specifically required for publication in JFMS Open Reports. Although not required, where ethical approval was still obtained, it is stated in the manuscript.
Informed consent
Informed consent (verbal or written) was obtained from the owner or legal custodian of all animal(s) described in this work (experimental or non-experimental animals, including cadavers, tissues and samples) for all procedure(s) undertaken (prospective or retrospective studies). No animals or people are identifiable within this publication, and therefore additional informed consent for publication was not required.
