5 Rare diseases in cats

The vet’s role is to ensure the health and wellbeing of their patients; to heal their wounds and treat their illnesses. Therefore, it can be challenging to be confronted by diseases or conditions that are not often seen in cats, requiring differential diagnosis and the solving of complex puzzles in order to treat their patients – especially felines. 

In this article, we explore five rare feline diseases or conditions, their symptoms, how the vet diagnoses them, and how they are treated or managed. 

Progressive retinal atrophy (PRA)

Progressive retinal atrophy is the gradual deterioration of a cat’s eyesight, caused either by retinas that do not develop properly (photoreceptor dysplasia, seen in kittens) or by the wasting of the retinal tissue, affecting the cones and rods in an adult cat’s eyes (photoreceptor degeneration). Over time, PRA leads to blindness. Progressive retinal atrophy is far more common in dogs than in cats, and, as with dogs, it’s a genetically inherited disease. It is seen most often in Abyssinian, Persian and Siamese cats.

Cats have excellent night vision, thanks to an abundance of rod cells and cone cells in the retina. Rod cells are responsible for the detection of light and movement, while cone cells detect colours. When the retina degrades, it directly impacts the functioning of the rods and cones, causing the cat to become night blind at first, and then lose their vision altogether. 

Initially, it’s very difficult to spot the subtle signs of a cat’s vision beginning to worsen. The perceptive cat owner may notice their cat’s eyes becoming more reflective at night and their pupils dilating more (in an attempt to let more light into their eyes). It’s usually only when the cat is bumping into obstacles or appearing to be anxious in the dark, or afraid to go into dark rooms, that owners notice that something is potentially wrong with their vision. They may also appear to be disoriented and not able to find their toys or food bowls. 

When diagnosing a cat with PRA, the vet will want to rule out any other diseases where deteriorating eyesight or even total blindness may be a symptom (such as in the case of feline leukaemia virus (FeLV) and feline immunodeficiency virus (FIV)). The vet may perform bloodwork and urinalysis, test the cat’s blood pressure as well as taurine levels. If PRA is suspected, the vet may refer the cat to a veterinary ophthalmologist for very specific testing, including electroretinography (ERG), which records electrical signals used to test retinal function.

There is no treatment or cure for PRA, which does not cause any pain or discomfort to the cat. It is important that owners manage the cat’s environment with their condition in mind. Don’t move the furniture around; block off access to staircases, swimming pools, and balconies; and keep the cat’s environment free of clutter. It should go without saying that they should not venture outside if they have trouble seeing. 

Cushing’s disease (hyperadrenocorticism)

Cushing’s disease or hyperadrenocorticism is more common in dogs and quite rare in cats. It is the excessive production (hyper-) by the adrenal glands (-adreno-) of the hormone cortisol (-corticism), which can be triggered by the improper functioning of the pituitary gland at the base of the brain or the adrenal glands themselves. It can also be caused when a cat is on corticosteroid drugs (like prednisone) for an extended period of time to keep allergies or asthma under control. When it’s brought on by medication, which happens very rarely in cats, it’s called iatrogenic hyperadrenocorticism. 

The symptoms of Cushing’s disease in cats include:

• excessive thirst and water consumption (polydipsia)
• excessive urination (polyuria)
• pot-bellied appearance
• increased appetite
• muscle atrophy/wasting
• weakness/lethargy
• poor coat condition with hair loss
• easy bruising
• thin, fragile skin
• slow wound healing

The vet will run a number of tests to rule out other conditions, as there is no single diagnostic test to confirm Cushing’s disease. Often, cats with the condition will have concurrent diabetes mellitus because excess cortisol can trigger or exacerbate insulin resistance. It’s therefore not surprising when blood tests show high blood sugar and high cholesterol (among other markers). One test – the urine cortisol:creatinine ratio (UCCR) – can rule out Cushing’s, so if it’s positive, the vet will be one step closer to a diagnosis. They will test for other markers and also perform an abdominal ultrasound to inform their diagnosis. The ultrasound can show enlarged adrenal glands or masses on the adrenals, the presence of any tumours, and whether the tumours have metastasised.

The treatment for Cushing’s disease will depend on what’s caused it. If caused by a pituitary tumour, careful consideration can be given to remove the pituitary gland and/or the adrenal glands. There are also medications that can be given, but not all cats respond well to them, so they will be prescribed on a case-by-case basis. Sometimes radiation therapy is performed to reduce a pituitary tumour. 

If Cushing’s is caused by an adrenal tumour, surgery can be performed to remove the tumour or, if surgery is not feasible, medication can be used to manage the condition. If the disease is iatrogenic hyperadrenocorticism, the steroid therapy causing it should be tapered off and stopped altogether. This means, however, that the allergies or asthma that necessitated the steroids in the first place, are likely to return and will need an alternative treatment. Adrenal support may be necessary after the steroids are stopped. 

If Cushing’s disease in cats is not treated, the prognosis is poor and the cat may die from infection (which is a common side effect of the disease) or diabetes. Often, the most successful treatment with the longest life expectancy is the removal of both adrenal glands and supportive treatment thereafter.

Feline cutaneous asthenia in cats

Feline cutaneous asthenia is also called Ehlers-Danlos syndrome and is referred to as a primary connective tissue disease, collagen dysplasia or fragile skin syndrome. An inherited genetic defect causes the cat to not produce enough collagen, and that which is produced has an abnormal structure. This means the collagen does not work the way it’s supposed to, so the cat’s ligaments, skin, and other connective tissues do not have the structural support that collagen normally provides. Cats’ skin is weak, loose and fragile, making them susceptible to injury and wounds. Feline cutaneous asthenia also affects the structural integrity of cats’ eyes, blood vessels and heart tissue. The cat breeds most affected by this condition are Himalayans, domestic shorthairs and domestic longhairs.

Since feline cutaneous asthenia affects the strength and elasticity of skin, ligaments, internal organs and blood vessels, the symptoms of this syndrome include:

• abnormal skin wounds in very young kittens (just from play)
• very obvious scarring from healed wounds
• saggy skin
• folding, redundant skin
• fragile skin that tears easily
• little skin elasticity
• swelling at joints, especially elbows
• joint laxity; dislocation
• hernias
• easy bruising/haematomas
• wide wounds that make the cat more prone to infection
• internal bleeding

Feline cutaneous asthenia is usually diagnosed using a skin extensibility test. This involves pinching the skin and stretching it to its full ability, with a notable lack of discomfort in the cat. The extended skin is measured and a formula is used to determine the presence and severity of the disorder. The vet will also take a patient history and take note of any scarring and bruising present.

The condition cannot be cured and if a severe case is diagnosed in a very young kitten, the prognosis is poor. The kitten or cat may experience chronic pain, in which case, it’s more humane to euthanise the animal. If the cat owner chooses to keep their cat, it may need to be the only animal in the home, and care must be taken to eliminate the risk of injury by covering sharp corners, blunt objects, and removing other risks. Extreme care must be taken to handle the cat very gently. The vet may even advise declawing them to prevent the cat from injuring themselves when scratching or grooming. The owner must be prepared for ongoing wound management, pain management, and skin treatment, keeping antibiotics available at all times.

Taurine-deficiency dilated cardiomyopathy and retinopathy

In the late 1980s, a link was made between the prevalence of dilated cardiomyopathy (weak heart muscle) and vision problems in cats, and a lack of taurine. Since then, taurine – an essential amino acid for optimal cat health – has been a key ingredient in commercial cat foods, to ensure that pet cats are receiving an adequate amount for their dietary needs. Cases of taurine-deficiency DCM and retinopathy have thus become rarer than in the past, but they do still occur. 

Taurine is essential for the proper development and functioning of the feline brain, heart, eyes, digestive and reproductive systems. The taurine provided in a high-quality cat diet is sufficient to ensure a domestic cat’s health and wellbeing. Taurine deficiency, then, is not an acute condition, but its effects are cumulative after months of inadequate taurine intake, by which time it can be fatal. Cats at risk of taurine deficiency are those fed an unfortified commercial cat food, home-made diets not prescribed by a veterinary nutritionist, vegetarian diets, and cats that are fed species-inappropriate food (such as dog food).

By the time a cat is assessed for the effects of taurine deficiency, the damage may already be done. The symptoms include:

• dilated cardiomyopathy – leading to insufficient blood circulation, difficulty breathing, weakness
• eye lesions and blindness
• deafness
• low appetite
• muscle weakness and atrophy
• infertility and reproductive problems 
• low immunity, resulting in recurring infection

When a cat is brought in to the vet’s office with the above symptoms, the vet will obtain a patient history – including information about their diet – to start their diagnostic process. They will do a physical examination, heart screening, eye tests, as well as a full blood panel, urinalysis and other laboratory tests. If the vet suspects a taurine deficiency, they may do a test to measure blood taurine levels and will make their diagnosis based on this and other advanced test results.

If a taurine deficiency is diagnosed early, it can be treated by supplementing the cat’s diet with taurine, as well as changing their diet to a high-quality, fortified cat food. If there is damage to the heart, eyes and/or other organs due to taurine deficiency, those conditions will need additional treatments, possibly for life. If the cat is already blind from the taurine deficiency, it’s impossible to reverse their blindness; similarly, if their heart muscle is thin and weakened, the condition cannot be reversed – only managed.

Feline papillomatosis

Feline papillomatosis is an extremely rare condition, characterised by the infection of a papilloma virus. It causes the growth of skin papillomas – or warts – which are small bumps with a scaly texture on the cat’s skin or in their mouth. Papillomas on healthy cats usually go away on their own when the cat’s immune system disrupts the virus’s replication and keeps the virus under control. Sometimes, however, the papillomas grow into skin plaques and, if they’re not treated promptly, can become cancerous. Papillomas in the cat’s mouth form in clusters of little bumps, but if they’re allowed to grow and become larger, they can affect the cat’s ability to chew their food or even swallow. A symptom of oral papillomas is excessive drooling.

Infection with the papilloma virus is spread by contact with an infected cat or a surface they have shed the virus on. The main symptom is the appearance of bumps and warts on the skin. These cats must be seen by a veterinarian as soon as possible.

The vet will examine the cat’s skin and may perform a fine-needle aspiration or biopsy, especially if they are concerned the papilloma is cancerous. The vet may give the cat three months to resolve the papilloma on its own (through a stimulated immune response), but if it does not go away, they may decide to surgically remove the wart. 

If the papilloma/s is treated early and either resolves on its own or is surgically removed, the prognosis is generally good. However, if cancer develops from an untreated papilloma, the prognosis may be uncertain or guarded.