Physicians generally have little knowledge of sensory distortions related to tastes and smells. Patients with a distorted salty or bitter taste in the mouth in the absence of food or drink (phantageusia) or a distorted rotten or chemical smell in the nose in the absence of any external odor (phantosmia) without any other neurological symptoms are usually not understood by their local medical physician. While phantageusia or phantosmia can be initially recognized as a manifestation of a seizure disorder (aura) or other serious disorder of the brain (e.g., tumor, arteriovenous malformation, etc.) once an EEG and brain MRI are found to be normal a psychological or psychiatric diagnosis is usually given to the patient.

Phantosmia and phantageusia are common sequelae among patients who lose taste and smell function. These symptoms require recognition of the anatomy and biochemistry from which they originate so that patients with these symptoms are not placed into a psychological waste basket.

To accomplish this we have developed a program whereby patients with these symptoms are evaluated not only by use of anatomical brain studies [magnetic resonance imaging of the brain (MRI)] but also by use of a novel functional technique called magnetic resonance spectroscopy (MRS) of the brain. By use of this technique several neurochemical components of the brain can be measured quantitatively using a non-invasive procedure.

By use of MRS several important brain metabolites can be measured: glutanic acid (Glu) — the main excitatory neurotransmitter in the brain, N-acetyl aspartase (NAA), a compound found exclusively in neurons and whose changes may reflect neuronal loss or impairment, choline (Chol), a compound which reflects cell membrane composition and whose changes reflect changes in membrane metabolism, creatinine (Cre) which reflects a measurement of energy metabolism, and gamma aminobutyric acid or GABA which is the major inhibitory neurotransmitter in the brain. This latter substance has been involved as a major factor in deafferentation-induced brain plasticity.

We measured these substances in brains of 28 healthy volunteers and in 19 patients with phantosmia and/or phantageusia. Localized two dimensional J-resolved spectra were acquired using a modification of the standard point resolved excitation in the steady state (PRESS) pulsing sequence.

Results of this study revealed that among patients with phantageusia and/or phantosmia levels of Glu, NAA, Chol and Cre were normal in all brain regions but GABA levels were significantly lower than normal in specific brain regions. These results prompted us to treat these patients initially with GABAergic drugs and subsequently with transcranial magnetic stimulation (TCMS).

After treatment we repeated these MRS studies to determine if levels of any of these brain metabolites had changed. Results demonstrated that there were no changes in levels of Glu, NAA, Chol or Cre but GABA levels had increased in each brain region in which it was lower than normal before treatment.

These results demonstrate that patients with phantageusia and/or phantosmia can exhibit a biochemical abnormality in GABA in their brain related to these symptoms and that treatments which increase brain GABA levels can inhibit these symptoms.

Thus, there is a biochemical basis related to symptoms of phantageusia and phantosmia. It is important for physicians to recognize this so that they do not dump these patients into a psychological waste basket. These symptoms must be evaluated critically such that if they exhibit a biochemical brain abnormality it can be identified and treated.

This study also emphasizes that phantageusia and phantosmia are not necessarily psychological manifestations of stress or age but reflect biochemical disorders which require careful evaluation just as do any other clinical symptoms such as headache or abdominal pain.

The major contributor to this program has been Dr. Lucian Levy, presently Chief of Neuroradiology, George Washington University Medical Center, Washington, D.C.

A portion of this study was previously published:

Levy, L.M., Henkin, R.I. Brain GABA levels are decreased in patients with phantageusia and phantosmia demonstrated by magnetic resonance spectroscopy. J. Comp. Asst. Tomog. 28:721-727, 2004.