Dr Brian Lipworth and colleagues studied 60 adults with inflammation of the nasal and sinus lining and moderate or large nasal polyps.
Patients had been referred to a Tayside rhinology clinic by their GPs and were assigned to receive either oral prednisolone 25mg a day or a placebo for two weeks.
All patients were then given fluticasone propionate nasal drops twice daily for 26 weeks.
Dr Lipworth and colleagues said they were not aware of any previous randomised controlled studies looking at the long-term effects of oral steroids in this setting.
Previous studies had either not included a placebo control or had only focused on short-term outcomes, they said.
The Dundee group found that, while there was a 0.1-unit decrease in polyp grade in the placebo group, there was a 2.1-unit decrease in the prednisolone group.
The researchers concluded: 'We found that an initial two-week course of oral steroid therapy followed by topical steroids seems more effective over 28 weeks than topical therapy alone in decreasing polyp size and improving olfaction for the treatment of CRS with nasal polyposis above grade 1, without sustained adverse effects.'
They added: 'Although further research is required to assess the efficacy and safety of this approach in other settings, we believe these results are an important step in developing robust treatment approaches for this common but relatively understudied condition.'
The researchers suggested that future studies could examine whether GPs should consider such an approach at first diagnosis of CRS with nasal polyposis.
They also said that short-term nasal decongestants may improve access of intranasal corticosteroids. These could therefore be assessed as a potential treatment, either alone or in conjunction with prednisolone, they added.