Murphy, a seven month old neutered male Bengal cat, was referred to the Langford Feline Centre at the University of Bristol for investigation of his lethargy and acute pain attacks. His problem first appeared four weeks earlier when his owner reported lack of energy, a ruffled coat, increased vocalisation and reluctance to jump or move. He seemed to be in pain when his owners tried to stoke or groom him. General examination at this stage revealed a painful thoracolumbar area of the spine on palpation. No major changes were detected on standard haematology and biochemistry tests, nor did radiographs reveal a cause of the pain over his spine. Murphy was treated with painkillers and a course of antibiotics.

A week later, Murphy still showed discomfort and attacks of acute pain, and neurological involvement was suspected. Murphy was therefore referred to Langford for further investigation and treatment.

Examination

At the Feline Centre Murphy's history revealed that he had been fed on only chicken and fish ever since he was acquired from the breeder at the age of eight weeks. On examination he was found to be in good bodily condition and was bright and alert. His legs were found to be short in comparison with his body and they rotated inwards. Murphy showed pain on palpation of the left front leg and thoracolumbar spinal area. In view of the dietary history we were suspicious that the clinical problems were related to a disease called hyperparathyroidism (an excess of activity of the parathyroid gland which produces hormones regulating calcium within the body).

This disease is seen in young cats fed an unbalanced diet, mainly based on meat, which has an inappropriate calcium/phosphorus ratio. In growing cats, a substantial amount of calcium is laid down in bone. If insufficient calcium is available in the food, the parathyroid glands produce more parathyroid hormone (PTH) in an attempt to maintain normal calcium concentration in the blood.

An increase in PTH will lead to an increase in blood calcium via three different systems:

• The PTH reduces excretion of calcium by the kidneys
• The intestines allow more absorption of calcium, via an increase in other hormones induced by the PTH levels.
• The PTH will increase bone resorption in order to release calcium from the bone.

Depending on the speed of growth of the cat (and thereby its calcium requirement) and the severity of the calcium deficiency, the increased bone resorption may lead to fragile bones and may cause clinical problems within one to three months. On presentation these cats will often have a disproportionately enlarged abdomen, because the growth of the skeleton lags behind that of the soft tissues. The animal may be reluctant to walk because of bone pain. There may be pathological or spontaneous fractures, abnormal alignment of bones, and bones may be painful on palpation. In severe cases there may be spinal cord compression due to vertebral fractures, causing a hind leg paralysis.

Blood tests revealed that Murphy did have a decreased level of calcium in his blood, which is unusual since blood calcium levels are usually maintained very effectively, and will only be decreased in severe cases.

Radiographs showed generalised decreased mineralisation, indicating bone fragility, and a growth plate fracture in his left front leg.

In the light of these findings, and considering the dietary history, it was likely that Murphy was suffering from nutritional hyperparathyroidism.

Murphy now needed a diet which we could be sure contained normal amounts of calcium, so we started him on a commercial cat food. A course of treatment with calcium tablets was started to supplement his calcium intake. Human calcium tablets can be given to cats, but not all cats will like them as they often have peppermint flavour! Some cats will do better on calcium powder added to their food. After three weeks the bones should be much stronger, however in the meantime special care is needed to prevent further fractures. The prognosis depends on the severity and the extent of the fractures, but is good in most cases. Narrowing of the pelvis may lead to later problems, such as repeated constipation, although this is unlikely in less severe cases which are treated promptly.

Murphy returned to Langford four weeks later, and was responding very well to treatment. He was happy in himself and very playful. His blood calcium was adequate and his radiographs showed improved mineralisation of the bones. He did show some deformities of scapulae, legs and pelvis but we do not expect these to become a problem.