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Only a short time ago, a diagnosis of feline infectious peritonitis (FIP) carried a devastating prognosis. The words alone could bring silence to any consult room and dread to any veterinary team. Yet, amidst the many tragedies of the COVID era, a groundbreaking advancement emerged in veterinary medicine—access to effective antiviral therapy for FIP. The rapid and dramatic improvement now possible for FIP cats treated with antiviral drugs such as molnupiravir has been nothing short of revolutionary.
This case explores a more extraordinary challenge, an unusual dual diagnosis and a remarkable outcome—a geriatric cat diagnosed with FIP and severe systemic cryptococcosis concurrently, a combination not yet reported in the literature.
Peanut (pictured left), a 12-year-old female-spey ragdoll x Tonkinese presented for a second opinion following several weeks of weight loss, inappetence, and general malaise. Her owner sought a second opinion at our veterinary clinic because of our recent experience with treating FIP cases.
On physical examination, Peanut was thin, with a body condition score of 2/5. Marked splenomegaly and thickened intestinal loops were palpable, and severe gingivitis was evident.
Initial bloodwork revealed marked hyperglobulinaemia at 71 g/L, a reduced albumin-to-globulin ratio, and persistent non-regenerative anaemia.
Abdominal ultrasound, performed by a specialist ultrasonographer, supported the clinical examination findings; a moderate splenomegaly with a mottled echotexture, diffuse thickening of the small intestines, and a concentrically thickened ileocecal valve. Cytology from splenic aspirates were unremarkable. At this stage, lymphoma, multiple myeloma, and FIP were all considered plausible diagnoses.
Because of the severity of Peanut’s dental disease and the possibility that oral pain was contributing to her inappetence, she underwent a dental procedure with extractions. Her early postoperative recovery appeared uncomplicated. However, five days later she presented with acute and profound neurological signs.
Peanut’s owner initially observed circling behaviour, which two days later had progressed to generalised ataxia, fluctuating ‘vague’ mentation, and absence of menace and palpebral reflexes. Ophthalmic examination revealed bilateral retinal haemorrhage and a blurred retinal appearance, raising concerns about retinal detachment or chorioretinitis. The patient remained active despite these findings.
Peanut was admitted to hospital for supportive therapy and observation. Her neurological signs occurred in an episodic way, lasting one to two hours, during which she appeared blind, disoriented, and failed basic proprioceptive tests. Interestingly, between episodes, her mentation and vision testing appeared to be normal.
During Peanut’s hospital stay, a scab-like lesion was found on her right forelimb. Fine-needle aspiration of this lesion revealed pyogranulomatous inflammation containing cryptococcal organisms. Serum cryptococcal blood antigen testing (LCAT) was strongly positive at 1:2048, confirming a systemic cryptococcal infection.
Considering a clinical picture with persistent hyperglobulinaemia, non-regenerative anaemia, and CNS dysfunction, a diagnosis of concurrent systemic cryptococcosis and presumed FIP was made—an exceptionally rare and challenging combination.
A note on diagnosing FIP
Definitive ante-mortem testing for FIP remains difficult. Diagnostic assays are costly, slow to return and yield results that are challenging to interpret. In contrast, modern FIP antiviral therapy is safe and typically produces a rapid clinical response, often within 12 to 24 hours. As such, in our experience, a therapeutic trial has become one of the most practical and reliable methods of supporting a diagnosis when clinical suspicion is high.
Treatment
After much consideration and owner consultation, treatment for both FIP and cryptococcus was initiated. Advanced brain imaging was discussed but ultimately avoided due to the risks associated with anaesthesia in such a neurologically unstable patient.
Antiviral therapy was initiated with oral molnupiravir at 50 mg twice daily, intended to be continued for a standard 84-day course. Fluconazole was started concurrently at 50 mg twice daily. Remarkably, within 12 hours, Peanut’s neurological signs resolved completely, her appetite returned, and she was discharged from hospital shortly after. According to her owner, Peanut did not experience further episodes of apparent blindness once home. Her rapid clinical improvement can only be assumed to be a response to the molnupiravir—confirming our diagnosis of FIP.
Amphotericin B was recommended as part of the antifungal protocol but was not immediately available due to supply issues in Australia. Treatment began one month later at another veterinary clinic more local to Peanut’s owner due to the intensity of treatment frequency and monitoring required.
The drug was administered subcutaneously twice weekly, with serial LCAT titres used to guide efficacy. After 15 doses delivered over 12 weeks, rising renal parameters prompted the permanent cessation of amphotericin B. Nephrotoxicity is a well-known complication of this drug.
Within a month of stopping amphotericin, the cryptococcal titre began to rise again. To improve treatment response, Peanut was transitioned from fluconazole to posaconazole, with the hope to further reduce the LCAT titre over time.
At the time of writing, Peanut has completed her full 84-day molnupiravir protocol and remains clinically well. She continues on daily posaconazole therapy, with her cryptococcal titres, renal and hepatic values carefully monitored at regular intervals. Her owner reports that she is thriving—gaining weight, eating enthusiastically, and enjoying an excellent quality of life.
Acknowledgements
Peanut initially presented for a second opinion at Progressive Vet Care in Melbourne, whose dedicated team continue to successfully treat many FIP felines.
Special thanks are extended to Dr Philip Lambley and the team at Rosebud Pet Vet, who administered Peanut’s in-hospital treatments and who continue to manage her ongoing care.
Dr Melyssa Cotton BSc BVMS
Dr Cotton graduated from Murdoch University in 2012 with a Bachelor of Science and a Bachelor of Veterinary Medicine and Surgery. After completing an internship in small animal medicine and oncology at The Animal Hospital in Perth, she moved to Melbourne to begin her career in small animal general practice.
She has since worked in a variety of clinics across Melbourne, including spending a wonderful nine years at Progressive Vet Care.
Dr Cotton recently transitioned out of general practice and now works with Sunset Vets in the palliative care space, supporting veterinarians, pets, and their families through terminal diagnoses and end-of-life challenges.
She is also passionate about educating the wider community on the value of palliative care and supporting the new generation of up-and-coming vets through mentorship.
