160 Surg Neurol 1993 ;40:160-3

Paroxysmal Bilateral Dysosmia Treated by Resection of the Olfactory Bulbs

J.M. Markert, M.D., D.O. Hartshorn, M.D., and S.M. Farhat, M.D. Department of Surgery, Section of Neurosurgery and Department of Otolaryngology, Head and Neck Surgery, University of Michigan Medical Center, and Catherine McAuley Health Center, Ann Arbor, Michigan

Markert JM, Hartshorn DO, Farhat SM. Paroxysmal bilateral Case Report dysosmia treated by resection of the olfactory bulbs. Surg Neurol 1993;40:160-3. P.G., a 37-year-old woman, was seen in November 1988. She reported a 17 year history of dysosmia with paroxysms of peculiar sensations of smell. These sensa- Dysosmia, or the distortion of olfaction, is most commonly tions were usually brought on by inhalation of other preceded by viral illness or head trauma, but has a variety strong odors, such as cigars, perfume, or onions; how- of etiologies. The precise nature of the disease process remains obscure. Medical management is largely empiric, ever, they also could be triggered by sudden turning of and has been aimed at treating underlying illnesses, re- the head, a big sniff, or emotional and physical stress. stricting triggering medications, as well as various phar- The common cold or flu would also exacerbate the sensa- macologic interventions. Successful eradication of a severe tion. Dysosmia paroxysms were described as unlike any case of persistent unilateral paroxysmal dysosmia with other odor, and always the same: of a hot, foul and resection of the ipsilateral olfactory bulb has been re- smoky nature on the right, and a sickeningly sweet, ported. We report here a case of bilateral paroxysmal dys- skunk-like odor on the left. Occasionally the episodes osmia, refractory to medical therapy, successfully treated would lateralize to a single side, but in general she expe- with bilateral olfactory bulb resection. rienced both sensations, on their respective sides, with each attack. Dysgeusia, or distortion of taste, did not KEY WORDS: Dysosmia; Parosmia; Olfactory bulb; Cranial seem to play a major role in the paroxysms, although nerve syndrome; Olfactory hallucinations she noted tastes compatible with the sensations of smell. The sensations were so powerful that she could not conduct any other activity during an attack, and had to simply rest until they subsided. Resting with her head in Dysosmia, or parosmia as it is also known, is the distor- a dependent position, with resultant lacrimation, would tion or perversion of the sense of smell most commonly occasionally relieve her symptoms. These episodes have seen after head trauma or viral illness [1,2]. Olfactory increased in severity and frequency progressively over hallucinations are sensations of odors, usually foul, that the years, and her ability to cope with them has declined. are frequently associated with temporal or uncinate lobe The patient's past medical history is significant for seizures or psychiatric illness. Frequent overlap occurs an episode of influenza during the Asian pandemic of between the two disorders. Paroxysmal dysosmia has 1968-69 which preceded the onset of her dysosmia been described elsewhere, and paroxysmal unilateral paroxysms by approximately three months. She addi- dysosmia successfully treated with ipsilateral resection tionally reports being struck in the head by two falling of the olfactory bulk has also been reported [6]. Here bricks at age seven or eight, apparently sustaining a brief we add to the limited literature currently available on loss of consciousness but no other sequelae. She suffered this topic with a case report of a patient who, after frequent episodes of otitis media as a child, with place- suffering many years from bilateral paroxysmal dysos- ment of bilateral myringotomy tubes. She smoked one mia, was successfully treated with bilateral resection of pack of cigarettes per day for approximately three years, the olfactory bulbs. but stopped smoking in 1973. She has a history of hypo- thyroidism for which she is receiving replacement therapy. Address reprint requests to:J.M. Markert, M.D., Section of Neuro- The patient sought help for her condition for many surgery, University of Michigan Medical Center, Taubman 2128, Ann Arbor, Michigan 48109-0338. years. She was seen at the Taste and Smell Clinic of Received July 24, 1992; accepted August 13, 1992. Georgetown University Medical Center where work-up

© 1993 by ElsevierScience Publishing Co., Inc. 0090-3019/93/$6.00 Paroxysmal Bilateral Dysosmia Surg Neurol 161 1993;40:160-3 was done, including sinus and skull radiographs, cranial Table 1. Disorders of Smell [3] computerized tomography as well as magnetic resonance Quantitative imaging; all were negative. She also had several electro- Anosmia: inability to detect odors encephalograms during dysosmic paroxysms, all of Hyposmia: decreased ability to detect which were negative. A repeat EEG showed minimal odors intermittent electrical disturbance in cerebral activity, Hyperosmia: decreased threshold for odor detection which was not felt to be significant, and no evidence of Qualitative epileptiform activity. Intranasal electrode EEG was also Dysosmia or Parosmia: distortion of odor perception negative. She was later evaluated at the University of Cacosmia: inappropriate detection of smell Connecticut Taste and Smell Center and found to have as malodorous minimal septal deviation, no intranasal disease, and mild Phantosmia: hallucination of odors Heterosmia: abnormal inability to distinguish unilateral hyposmia on the left side (70% of normal between odors function). She was normosmic on the right with 90% of normal function. Taste was normal. Electrolytes, SGOT, SGPT, IgE, CBC with differential, and urinalysis were all within normal limits. Thyroid function tests demon- ported by the National Advisory of Neurological and strated only a mild elevation in T4. No cause for her Communicative Disorders and Stroke Council [16]. Dis* disorder was identified. She was treated with various orders of smell are classified as "-osmias." The nomencla- medical regimens, including phenytoin, phenobarbitol, ture in the literature is inconsistent; however, Table 1 thioridazine, and haloperidol, propranolol, depakene, gives a general overview. In addition, these disorders and papaverin. Mild improvement was noted only with are subclassified as general (affecting all odors), partial the haloperidol, and only at doses that resulted in exces- (affecting some, but not all), or specific (affecting only sive somnolence. She was also treated with intranasal one or a very limited number). They may be either corticosteroids and zinc supplementation without sig- constant or intermittent in nature [2,3,15] (Table 1). nificant improvement. The anatomic origin for abnormalities in smell per- Based on an earlier report of a similar unilateral case ception may be peripheral, central or combined. Periph- [6], we offered the patient the option of a craniotomy eral abnormalities may arise at the level of the nasal with bilateral resection of the olfactory bulbs. In January mucosa or the olfactory nerves. Central abnormalities 1990, she underwent the proposed operation. Although commence at the level of the olfactory bulb, which may a pterional approach was initially considered, it was felt function as a primitive locus for limited odor discrimina- that a transfrontal approach would give optimal expo- tion. Continuous background electrical activity in the sure. A single bone flap was raised in the frontal region bulbs is increased by olfactory stimulation. The olfactory across the midline. The dura was opened bilaterally and tracts become medial and lateral striae which travel to the superior sagittal sinus left intact. The right frontal the cerebral hemispheres bilaterally; there is no thalamic lobe was retracted laterally, and its medial aspect fol- relay. The olfactory cortex in man occupies only a small lowed down to the underlying cribriform plate. The portion of each anteriomedial temporal lobe, the pyri- large, pale yellow olfactory bulb, normal in appearance, form cortex [ 1]. was immediately noted and resected. The left frontal Dysosmias have also been classified as central or pe- lobe was then retracted laterally with resection of that ripheral in nature [15]. Central dysosmias include: (1) olfactory bulb undertaken in an identical fashion with illusions of smell perceived in certain medical conditions similar findings. Microscopic examination was normal, including pregnancy; (2) olfactory hallucinations as expe- with no evidence of tumor, inflammation, vasculitis, am- rienced by psychotic patients; and (3) uncinate fits, or yloid, or other conditions. hallucinations of smell associated with temporal lobe The patient recovered from her operation without seizures. Peripheral dysosmias include cacosmia, con- incident. She noted complete anosmia postoperatively, stant or periodic episodes of bad smell resulting from with total relief of her symptoms immediately. Noxious abnormalities of the upper airway and nose or from challenges similar to those which would have immedi- inflammatory conditions such as sinusitis or tonsillitis. ately induced dysosmia preoperatively had no effect. Essential parosmia exists when stimulation of the sense She has been followed for 15 months without recurrence of smell results in a perverted sensation, usually of a of her symptoms. foul odor. It can result from infections, cranial injury, or exposure to either systemic or local toxins. Most cases Discussion of essential parosmia, however, are of unknown etiology. Approximately 2 million Americans suffer from disor- This disorder has been compared to trigeminal neuralgia ders of taste and smell, according to a 1979 study re- and other cranial nerve paroxysmal syndromes; as it 162 Surg Neurol Markert et al 1993;40:160-3 shares many of the common features of these condi- Previous surgery or radiation can result in disorders tions, including precipitating stimulus (usually of a me- of the sense of smell, most frequently hyposmia. These chanical nature), characteristically brief attacks, and a are usually associated with therapy directed at the nasal cranial nerve which may or may not be demonstrably region. Laryngectomy can decrease the acuity of the damaged [6]. sense of smell by decreasing the active passage of air Dysosmia and anosmia have various etiologies. The through the nose, and preventing adequate stimulation single most common cause of disorders of smell is a viral of the olfactory epithelium [2,11]. Coronary bypass has infectious syndrome [2]. Many of these disorders have also been associated with parosmia [ 10]. been traced to specific influenza pandemics, notably to Drugs are another frequent offender; clofibrate, am- the "Hong-Kong" flu pandemic of 1968-69 [4]. Other photericin B, carbimazole, calcium channel blockers, infections associated with subsequent dysosmia or hy- and many other medications have been associated with posmia include meningitis, viral hepatitis, polio, yellow dysosmia. Many chemicals and organic solvents have also fever, smallpox, typhoid fever, diphtheria, plague, mea- been linked to cacosmia [2,5,8,9,13]. sles, and impetigo. Return of normal function is often Systemic illnesses such as diabetes, chronic renal noted after several weeks or months. disease, cirrhosis, malnutrition, Addison's disease, con- Blunt head trauma is a frequent cause of these disor- genital adrenal hyperplasia, hypothyroidism, and ders, with loss of smell presenting more frequently than various other endocrine abnormalities and autoim- its distortion. The putative mechanism involves shearing mune syndromes can also distort the sense of smell of the olfactory nerves at the cribriform plate; subse- [2,3]. quent axonal regeneration is usually minimal, and recon- A lack of understanding of the precise pathophysio- nection of receptor cells with the olfactory bulb further logic processes contributing to dysosmias and the dispar- hampered by scarring [1,5]. Recovery of normal func- ity of the underlying etiologies renders treatment of tion may occur after weeks or months, but frequently these disorders obscure. Some success has been obtained damage is permanent. Tumors or other irritative lesions can lead to a dys- from treatment of an underlying medical condition or function of the sense of smell. Meningiomas are the discontinuing contributing medications. Pharmacother- most commonly involved intracranial tumors, particu- apy has been widely empiric; our patient was treated larly when located along the suprasellar region, sphenoid with a variety of medications including anticonvulsants, ridge, frontal parasagittal region, or the olfactory groove antipsychotics, steroids, beta blockers, and corticoste- [2]. Other intracranial tumors that can affect olfaction roids, all without success. Until a better understanding include gliomas, craniopharyngiomas, neurofibromas, of this disease process exists, surgical intervention may schwannomas, xanthogranulomas, tuberculomas, der- be appropriate for treatment of selected severe cases of moids, encephaloceles, and large aneurysms of the inter- this condition not responsive to medical and pharmaco- nal carotid or anterior communicating arteries. Hydro- logic management. cephalus forcing the floor of the third ventricle downward can also account for such dysfunction [2,3,7,12]. Intracranial tumors within the temporal lobe, Conclusion or impinging on it, can cause olfactory hallucinations Disorders of smell, including the syndrome of parosmia, with an incidence approaching 20%. Many of these tu- may have many clinical etiologies. These must be care- mors are associated with temporal lobe epilepsy and fully evaluated, as they can be clues to other illnesses uncinate fits. Olfactory hallucinations have also been or lesions. Many cases will remain obscure in origin, but reported with lesions in other areas of the brain acting even these usually remit in a matter of months. For the through association bundles and thus triggering the tem- patient with persistent, severe paroxysmal dyosmia of poral lobe syndrome [14]. unknown origin, refractory to medical management, sur- Psychiatric disorders are associated with olfactory" hal- gical sectioning of the olfactory bulk has been shown to lucinations, most commonly with major depressive epi- relieve the condition in at least one unilateral case and sodes, schizophrenia, confusional states, and acute psy- can now be viewed as a potential therapeutic option for chosis. In general, the perceived odor is unpleasant. the bilateral occurrence as well. Recognition of these hallucinations has apparently in- creased in recent years with a heightened level of aware- ness amongst mental health professionals, and indeed, References dysosmia is now recognized as a potential mask of de- 1. Adams RD, Victor M: Disorders of smell and taste. In: Principles pressive illness [2,9]. of neurology. New York, McGraw Hill, 1989:181-9. Paroxysmal Bilateral Dysosmia Surg Neurol 163 1993;40:160-3

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