Paradoxical low nasal nitric oxide in nasal polyposis

Nitric oxide (NO) is synthesized in the respiratory tract. Three isoforms of NO synthase have been described in man, with the inducible form related to inflammatory disease. In the paranasal sinuses constitutive production of nitric oxide has been demonstrated, with levels of 20-25 p.p.m. being found in sinus puncture. Nasal polyposis is a chronic inflammatory condition in which inducible nitric oxide synthase (iNOS) expression is elevated in nasal polyp epithelium.

1. Measurement of upper airway nitric oxide in nasal polyposis patients compared with those with allergic rhinitis, and with normal controls. 2. To assess the effect of polyp treatment on nasal NO levels.

NO levels (parts per billion) were measured in nasal and pulmonary exhaled air using a LR 2000 Logan Sinclair nitric oxide gas analyser. This utilizes the chemiluminescence principle. Eighty-two patients were studied: 44 with rhinitis, but without polyps, and 38 with nasal polyps. NO levels were compared with those of 20 normal controls. In 23 further polyp patients, levels were measured pre- and post-treatment and the changes were compared with alterations in polyp size, as assessed by rigid nasendoscopy.

Nasal NO levels were significantly lower (Kruskal-Wallis, P = 0.000, chi2 = 27.5, d.f. = 3) in patients with polyps than those found in uncomplicated allergic rhinitis. NO levels were correlated directly with extent of polyposis as graded by the Lund-McKay index. Successful treatment, with reduction in polyp volume, was associated with a rise in NO levels (P = 0.042).

NO levels are low in nasal polyposis, despite high levels of iNOS, possibly related to blockage of the ostiomeatal complex and failure of NO generated constitutively in the sinuses to reach the nasal airway. A rise in the NO levels is seen with successful polyp treatment, and is proportional to the reduction in endoscopically assessed polyp size, suggesting that with both medical and surgical therapy, the ostiomeatal complex obstruction is decreasing. We propose the following scenario. Nasal NO levels are the result of two processes: inducible NO production by inflamed nasal mucosa plus constitutive sinus mucosal production, detectable in normals. In uncomplicated allergic rhinitis with patent sinus ostia NO levels tend to be elevated, but when inflammation is sufficient to obstruct sinus ostia (as in nasal polyps), NO levels fall because sinus NO makes the major contribution.