Identify specific thoracic deformities

FCK occurs sporadically in all breeds of cats including domestic short hairs, and is therefore of concern to every breed and breeder in the cat fancy. It can affect kittens without warning, from parents who have shown no sign or indication of producing kittens with the problem, and from repeat matings that have previously produced only healthy kittens. It can affect only one kitten, or it may affect whole litters; kittens may recover or they may die. There are few references to this condition in the veterinary literature; as a result veterinary professionals do not always recognise the condition, and breeders sometimes have to find out about it by themselves when they discover they have a kitten that they think is affected.

What are thoracic deformities?

The thoracic deformity best known among cat breeders is FCKS, or Flat-Chested Kitten Syndrome, but FCKS is just one condition: breeders with flat-chested kittens are usually concerned about the flat ribcage, and may not be aware that a kitten may also have kyphosis (a dip in the spine behind the shoulder-blades) or pectus excavatum (an inverted sternum) as well. For this reason the research envisioned by the THINK project embraces all thoracic deformities, since they may be related. In the course of our investigations other thoracic deformities may become apparent. Equally FCKS may be the end product of a variety of different processes such that the causes of FCKS in one breed may not be the same as in a different breed thus requiring different preventative measures and treatment regimes.

Some vets and breeders use the term pectus excavatum (PE) to describe FCKS, this is incorrect, as the two are in fact different conditions and can occur independently or simultaneously: a flat chest is not the same condition as an inward-turning sternum. Kyphosis, a dip in the spine just behind the shoulders, similarly may appear by itself or in conjunction with FCKS. By itself it does not seem to be life-threatening, but it can affect the growth of the front half of a kitten's body. This radiograph shows the ribcage (or thorax) of a kitten with PE, FCKS and kyphosis; this kitten survived all these problems!

X-ray of FCK

Comparison of normal, FCK and PE

In FCKS the underside of the ribcage flattens and sometimes curls inwards. In extreme cases, the kitten will start gasping for breath and will die if untreated. There are degrees of flat-chestedness, with kittens in the same litter being affected to varying extents. If the ribcage collapses inwards, lung and heart function become compromised. Many slightly flat-chested kittens go unnoticed and recover on their own. Some kittens that appear to do well at first nevertheless die. The two diagrams here, showing the difference between pectus excavatum and FCKS were produced in a veterinary study that was commissioned by the Burmese Cat Club. FCKS is not limited to cats: piglets suffer from flat chests and so do humans. Although swimmer puppies and kittens can look similar to FCKS, deformities of the rib cage are not part of the primary disorder. If we can define the underlying processes that lead to a flat chest, there is the potential to help many other animals and people.

Kyphosis and PE are both deformities of the bone, and cannot usually be corrected, although surgical correction of PE is reported in older kittens. FCKS is thought to be associated with the muscles between the ribs (intercostal muscles) and possibly the diaphragm, resulting in an otherwise normal ribcage being pulled into an abnormal shape thus preventing correct chest movement. In FCKS the whole volume of the chest cavity is reduced, affecting the amount of air that is moved in and out of the lungs with each breath (tidal volume). Less oxygen is delivered to the blood stream and the kitten tries to compensate by breathing faster. As a result, severely affected kittens appear to be panting.

How can I tell if a kitten has FCK or another thoracic deformity?

typical FCK

Bony deformities are reasonably easy to spot: PE is not always very obvious, but a kitten with the condition often has a dip in the centre of its chest (see illustration below, right), like the entrance of a funnel, hence its lay name, funnel chest. PE, Kyphosis, & FCKS become apparent shortly after birth: if kittens are checked frequently it is possible to see almost immediately when the rib-cage has flattened or dipped. Flattening is often not present at birth but will usually become apparent within 25 days; the point at which it is noticed may be related to the severity. Flattening can appear to occur suddenly over a few hours or gradually worsen over several days. By feeling the sides of the ribcage with the fingers it is possible to detect the flattening before it is associated with obvious breathing changes as there is a ridge running long ways at the sides of the ribcage. Flattening can also be detected by comparing the dimensions of the chest with other kittens in the litter. In all kittens there is a slight ridge running along the ribcage where the bony rib meets the cartilage that attaches to the sternum. This is more obvious in some kittens but does not necessarily mean that they are flat chested.

PE kitten

Kittens with thoracic deformities use up far more energy breathing and moving than normal kittens. Often an early sign that something is wrong is a failure to gain weight because they are too tired to fight for a teat, to suckle for long enough or are reluctant to feed as they cannot breathe and swallow at the same time. Many breeders have found that supplement feeding seems to help FCKs, even if they seem to be feeding normally from the mother.

Knowing what FCKS looks like in a diagram does not always help to work out if a kitten is suffering from the condition. However, a reasonably fresh banana can give some idea of what a flat ribcage feels like. Hold the banana with the flattest side downwards (usually on the inside of the curve), and draw your hand upwards. The outside of the skin has two clear ridges at the lower edge, and the bottom is flatter than the sides and top. This is almost exactly what a mildly flat chest feels like (even down to the size) only with a covering of fur.

Normally the flat chest is simply that: flat. But if the condition is severe the sternum and ribcage can be collapsed into the chest cavity. This can compromise the function of the heart and lungs and potentially could affect the development of the cardiorespiratory system. This collapse is one reason the condition is sometimes misdiagnosed as pectus excavatum, but the collapse affects the whole length of the rib cage rather than being centred on the most backward point (xiphisternum) as in PE. Kittens with this advanced form of FCKS will not usually survive without active intervention.

There is another condition (apparently unrelated to FCKS) in which the sternum grows outwards, and may 'float', and though this apparently has no health implications, it is considered a veterinary fault. There are also other deformities that are not described here, which may or may not be related.

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