Pulmonary mass‐like lesion caused by Toxoplasma gondii in a domestic shorthair cat

Abstract A 2‐year‐old male neutered domestic shorthair cat underwent investigations for acute onset of lethargy, hyporexia, and cough. Computed tomography of the thorax identified a large mass‐like lesion in the left cranial lung lobe and bilateral pleural effusion. Thoracotomy and left cranial lung lobectomy were performed. Histopathology of the pulmonary mass was consistent with a localized Toxoplasma gondii pneumonia, confirmed by positive polymerase chain reaction on the affected lung lobe. After adjunctive medical management with a 28‐day course of clindamycin (12.5 mg/kg PO q12h), clinical signs resolved and repeat thoracic radiographs documented no abnormalities. The cat remains clinically well 1 year after surgery.


| CASE DESCRIPTION
It had been adopted from a rescue center approximately 4 months before presentation and had regular outdoor access. On physical examination at that time, the cat was bright, alert and responsive. It was tachypneic with a respiratory rate of 44 breaths per minute and a restrictive breathing pattern. Pulmonary parenchymal sounds and heart sounds were decreased ventrally, bilaterally, more notably on the left side. Heart rate and rectal temperature were within normal reference intervals (RIs). No other abnormalities were present on physical examination. Thoracic radiographs, reviewed by a Diplomate of the European College of Veterinary Diagnostic Imaging, revealed moderate pleural effusion bilaterally and a pulmonary mass-like lesion associated with the left cranial lung lobe. There was a second area of increased pulmonary opacity in the right hemithorax associated with the right middle lung lobe (Figure 1). Peripheral capillary oxygen saturation (SpO2) was 98%. Ultrasound-guided thoracocentesis was performed for diagnostic and therapeutic purposes, and 50 mL of slightly turbid yelloworange effusion was drained from the left hemithorax. The effusion was a protein-rich transudate (total nucleated cell count was 1.4 × 10 9 /L and total protein was 3.0 g/dL) with a population of atypical large mononuclear cells. There was no aerobic or anaerobic bacterial growth. There was a marked leukopenia of 2.1 × 10 9 /L (RI, 7.7-19 × 10 9 /L), comprised of a marked neutropenia (0.65 × 10 9 /L; RI, 2.5-12.5 × 10 9 /L) and moderate lymphopenia (0.9 × 10 9 /L; RI, 1.5-6.5 × 10 9 /L). No white blood cell morphological abnormalities were identified. There was mild hypoproteinemia of 5.1 g/dL (RI, 5.5-7.8 g/dL) To further investigate the pulmonary mass-like lesion seen on thoracic radiographs, a contrast computed tomography (CT) scan of the tho-

| DISCUSSION
This is a case of localized pulmonary toxoplasmosis in a cat. Pulmonary toxoplasmosis is documented previously in cats. However, in other reported cases, the disease presented as part of disseminated toxoplasmosis, with multiple pulmonary lesions or diffuse alveolar or interstitial pulmonary changes, with or without pleural effusion. [1][2][3] Affected cats have an identifiable cause of systemic immunosuppression that predisposed them to develop clinical toxoplasmosis, such as the administration of chemotherapy, 1 cyclosporine treatment, 2,4 or pregnancy. 3 Conversely, the cat in this report had a single large pulmonary lesion and had no identifiable cause for immunosuppression. some cats do not have detectable IgM until 4 to 10 weeks after infection, and up to 20% of infected cats never develop detectable IgM. 9,10 Unfortunately, the IgG titer on both occasions it was measured exceeded the maximum detectable dilution tested by the laboratory.
Had further dilutions been available, assessing the dynamics of the IgG titer over time would have been helpful for characterizing the chronicity of the immune response and timeframe of possible exposure. It is possible the cat in this report had a novel T gondii infection caused by ingestion of bradyzoites from rodent prey or undercooked meat. An alternative explanation is that this cat's toxoplasmosis was caused by reactivation of a latent infection, triggered by an unidentified immunosuppressive stress.
When a pulmonary mass-like lesion is documented on thoracic radiography or CT, the primary differential is neoplasia; the most common primary lung tumor in cats is an adenocarcinoma, and less common neoplasms include squamous cell carcinoma and anaplastic carcinoma. 11,12 Previous radiographic findings of pulmonary toxoplasmosis include diffuse interstitial to alveolar patterns and pleural effusion 2,13 Description of CT findings of pulmonary toxoplasmosis in cats are limited. One report describes a cat with multiple pulmonary nodules measuring up to a maximum of 15.7 mm diameter, resembling metastatic neoplasia. 1 CT features of human patients with pulmonary toxoplasmosis include ground glass opacities, bilateral smooth septal and peribronchovascular thickening, atelectasis, random nodules, lymph node enlargement, and pleural effusion. 14 The decision was taken to pursue surgical management in the first instance because of the extensive nature of this cat's disease. The imaging features and cytological assessment of the mass lesion raised concern that clindamycin alone would not penetrate all aspects of the suspected granuloma nor result in clinical resolution. Clinical and radiologic improvement occurs in human patients with T gondii mass lesions that are treated medically without surgical debulking. [15][16][17] However, in the absence of other documented cases of solitary T gondii pulmonary mass-like lesions in cats, medical treatment alone was not recommended. Adjuvant medical treatment was administered to increase the likelihood of clinical resolution, given that toxoplasmosis is usually a multisystemic disease. The authors acknowledge that even though apparent clinical resolution of this cat's T gondii granuloma was obtained, persistence of organisms in tissue cysts is likely, and clinical signs could recur in future in the event of immunosuppression.

ACKNOWLEDGMENT
Open access funding provided by IReL. WOA Institution: University College Dublin Blended DEAL: IReL.

CONFLICT OF INTEREST DECLARATION
Authors declare no conflict of interest.

OFF-LABEL ANTIMICROBIAL DECLARATION
Clindamycin was used off-label to treat toxoplasmosis.

INSTITUTIONAL ANIMAL CARE AND USE COMMITTEE (IACUC) OR OTHER APPROVAL DECLARATION
Authors declare no IACUC or other approval was needed.

HUMAN ETHICS APPROVAL DECLARATION
Authors declare human ethics approval was not needed for this study.