Doctors warn that conditions such as multiple system atrophy and progressive supranuclear palsy are often difficult to diagnose because the telltale signs, which include tremors and slow movements, are similar to those of Parkinson’s Disease.

Now researchers in the US have found that PET (positron emission tomography) brain scans, which show brain activity, can help determine which of the three forms of Parkinsonism patients are suffering from.

This follows the publication of new recommendations in Scotland that people suspected of having the illness should receive a diagnosis and, if confirmed, receive care from an expert consultant rather than a GP who may not be familiar enough with Parkinson’s.

Scientists at The Feinstein Institute for Medical Research in New York, led by Dr David Eidelberg, said better diagnosis would mean that fewer people would receive ineffective treatments.

Professor Angelo Antonini, of the Venice and Parkinson Institute in Milan, warned the results were “no replacement for thorough clinical investigation”.

But he said: “The clinical and research relevance of these findings should not be underestimated.

“Neuroprotective and disease-modifying drug research is intensifying and results mostly rely on accurate early diagnosis.”

There are between 160 and 200 patients with Parkinson’s Disease per 100,000 people in Scotland, according to the latest figures, and the number of cases is expected to increase by up to 30% over the next 25 years.

No single diagnostic test is currently available and evidence shows that some people with Parkinson’s do not receive the treatment they need to relieve their symptoms while others may be wrongly diagnosed with the disease and given drugs they don’t need.

The new research, published in The Lancet today, focuses on ways to distinguish between idiopathic Parkinson’s Disease and less common forms of Parkinsonism, which include multiple system atrophy and progressive supranuclear palsy.

Some 167 patients, who were monitored for two years, underwent PET scans and the scientists developed a new procedure to distinguish between the three conditions.

The researchers found that 98% of patients with positive test results for Parkinson’s Disease were correctly diagnosed, compared with 97% for multiple system atrophy and 91% for progressive supranuclear palsy.

They said: “Accurate early diagnosis of Parkinsonian disorders is important for several reasons. First, prognosis for different disorders differs greatly: for example, idiopathic Parkinson’s Disease does not substantially shorten a patient’s lifespan, but patients with multiple system atrophy and progressive supranuclear palsy typically have a life expectancy of only several years after diagnosis.

“Second, some treatments have different outcomes: for example, deep brain stimulation is usually effective in patients with idiopathic Parkinson’s Disease, but not in patients with atypical parkinsonism.

“Third, clinical trials of potentially disease-modifying drugs might include misdiagnosed patients.”

They added: “Automated image-based classification has high specificity in distinguishing between Parkinsonian disorders and could help in selecting treatment for early stage patients and identifying participants for clinical trials.”

On Thursday, the Scottish Intercollegiate Guidelines Network issued new recommendations that patients should be diagnosed and receive ongoing care from a consultant with expertise in motor disorders, rather than a GP who may not be familiar enough with the disease to distinguish it from other conditions.