Study on difference in olfactory response in dysosmia patients

Using 1952 dysosmia patients, we studied the difference in olfactory response to 5 types of odorous substances used in the standard olfactory acuity test in Japan--beta-phenyl ethyl alcohol, methyl cyclopentenolone, isovaleric acid, gamma-undecalactone, and scatol. Olfactory dysfunctions included 887 patients with chronic paranasal sinusitis, 255 with allergic rhinitis, 326 with common cold sequela, 77 with complications from head injuries, 28 with drug-induced dysosmia, 39 with congenital dysosmia, 257 with dysosmia of unknown etiology, and 83 miscellaneous. The standard olfactory acuity test before treatment indicated that 82 patients detected only one odor within the detection threshold and 157 within the recognition threshold; 40 responded only to isovaleric acid at the detection threshold and 101 at the recognition threshold. Both figures were significantly greater than those who responded to other odors (p < 0.01). No specific trends were noted in etiologies of dysosmia that allowed smelling of isovaleric acid only either at the detection or recognition threshold. Among those whose olfactory thresholds were judged to be scaled out against all 5 odorous substances, 552 were rated as scaled out at the detection threshold and 630 at the recognition threshold. During post treatment, 33 scaled out at the detection threshold and 32 scaled out at the recognition threshold improved enough to smell 1 type of odor. Of these, 15 scaled out at the detection threshold and 13 scaled out at the recognition threshold became able to smell only isovaleric acid. Those becoming able to smell only isovaleric acid either at the detection or recognition threshold, significantly outnumbered those becoming able to smell other odors (p < 0.01). No outstanding cause of dysosmia was seen in those able to smell isovaleric acid. This data indicates that olfactory function for detecting isovaleric acid is relatively resistant to disease and is most likely to be restored. The difference in olfactory response of patients with olfactory dysfunction such as those above may be due to variations in the number of olfactory receptor proteins for specific odors within olfactory cells or different responses to the type of molecules of odor-emitting substances.