If people go to their doctors with a swollen, painful joint, they may be told that they have gout. The diagnosis of gout is usually fairly simple. The joint most often involved is that at the base of the big toe; it becomes painful, slightly swollen, red and warm, and often improves with full doses of an anti-inflammatory non-steroid drug (NSAID). To be quite sure of the diagnosis, the doctor often measures the uric acid level in the blood. Gout is caused by deposits of crystals (monosodium urate) in cells that line the joint cavity. Taking some joint fluid out with a needle can confirm the diagnosis, as the typical urate crystals can be seen under the microscope.

Sometimes, however, the crystals are not caused by an increased blood uric acid, but are made up of a calcium salt (calcium pyrophosphate dihydrate, or CPPD). In this case, the condition is called pseudogout. How does pseudogout differ from classical gout? One difference is that the first attack typically strikes the knee rather than the joint of the big toe, and in two-thirds of cases more than one joint is affected. Now some Italian physicians have examined the time of the year when attacks are most frequent, and found further differences between the two diseases.

All the case records of people attending St Anna Hospital in Ferrara, Italy, with an acute attack of joint inflammation over an 8-year period were examined. In all of those selected, a sample of joint fluid was taken and examined microscopically. This allowed the cases to be divided into classical gout (urate crystals) and pseudogout (CPPD crystals). The date of hospital attendance allowed them to be categorized into spring, summer, fall, or winter attacks.

Over the 8-year period there were 210 acute gout attacks - 93% in men and 7% in women. The average age of the men was 56 and that of the women 68 years. During the same period, there were 179 attacks of pseudogout registered - 32% in men and 68% in women. The average age of the men was 67, and of the women 72 years.

These results show that gout occurs far more often in men than in women, while pseudogout occurs equally in men and women. Moreover, gout occurs in both men and women at a slightly earlier age than pseudogout.

When the time-of-year of the attacks were analyzed, it was found that there was an increased incidence of classical gout cases in the spring. 36% of attacks were recorded in the spring, 27% in winter, 20% in summer and 16% in the fall. With pseudogout, there wasn't any such obvious seasonal distribution. 29% of cases were reported in the fall, 25% each in the winter and summer, and 21% in the spring.

What does this mean for the patient with one or more painful inflamed joints? Not everyone relishes the idea of having a needle stuck into the joint to get fluid for an exact diagnosis. Classical gout can be diagnosed with the help of a blood uric acid level determination, and the initial treatment - an NSAID, or possibly colchicine, as painkillers - can be equally effective in gout or pseudogout. However, if attacks are frequent and the painkillers are not sufficiently effective, it may be necessary for drugs to be taken to treat the metabolic upset causing an increased uric acid (uricosurics). Before this more radical approach is undertaken, one should be sure that the disease is, indeed, gout, rather than pseudogout.

Perhaps, quite commonly, people who have been told they have gout will undertake dietary changes, such as the abandonment of purine-containing foods. Again, before this somewhat drastic measure is taken, people should make sure that they really have gout, and not pseudogout.

The cause of pseudogout is unknown, although it is sometimes seen in people with raised serum calcium levels (due to disease of the parathyroid gland), increased iron in the tissues (a disease known as hemochromatosis) and when there are low magnesium levels in the blood. Treatment, therefore, should be aimed at any cause like this that can be found. The classical dietary modifications recommended for gout victims, however, are unlikely to be helpful in the case of pseudogout.