Diagnostic dilemma: After taking a medicine for years, a man suddenly had weird changes in his taste that made food disgusting

The patient: A 61-year-old man in Japan

The symptoms: The man visited a hospital because two months earlier, some foods and beverages began to taste extremely unpleasant to him. Over time, more foods had become difficult for him to stomach. Sour and salty flavors were the first to trigger disgust. Oily foods were next, followed by fresh vegetables, cold water and juice, warm water and, finally, sweets.

The man ate less due to the taste aversions, and he unintentionally lost a few pounds. He told doctors at the hospital that he felt lethargic, they wrote in a report of the case.

What happened next: The patient, who was a physician himself, reported that eight years ago, he had been diagnosed with bipolar disorder. For the prior three years, he had been managing the condition with lithium, a mood stabilizer commonly used to treat bipolar disorder.

He was taking a prescribed dosage of 800 milligrams per day and historically hadn't had any unusual side effects. (This is slightly higher than the typical dose recommended for chronic management of bipolar disorder, but that said, doctors may tweak patients' doses based on their individual needs.)

The diagnosis: Doctors performed bloodwork and found that the level of lithium in the patient's blood was 1.28 milliequivalents per liter (mEq/L). Safe levels of lithium are between 0.6 and 1.2 mEq/L; any higher than that can cause a condition called lithium toxicity, which can be fatal if untreated.

When the doctors checked the man's medical records, they found that prior to the onset of his symptoms, the levels of lithium in his blood were between 0.4 and 0.9 mEq/L. In the report, the authors did not investigate the cause of the toxicity, nor did they hypothesize as to why lithium was accumulating in the patient's blood.

The treatment: The doctors told the man to stop taking lithium, and they instead prescribed another mood-stabilizing drug, called valproate. As the lithium levels in his blood dropped, the patient's energy returned and the foods and beverages that previously disgusted him recovered their normal flavors. Notably, this happened in the reverse order that their flavors had changed.

At a follow-up visit one year later, the man was still taking valproate and his symptoms of fatigue and taste changes had not returned.

What makes the case unique: Although they're uncommon, side effects of lithium use can include confusion, increased thirst, frequent urination, irregular or slow heartbeat, tiredness and weight gain. Rarer side effects include dizziness, headaches, vision problems and heat loss in the arms and legs. Lithium toxicity, also known as lithium intoxication, is known to increase the risk of these adverse symptoms.

Changes in a patient's sense of taste while taking lithium have been recorded in just a handful of reports dating to the 1970s and 1980s. One patient lost the ability to taste salt, while another "noticed a strange and unpleasant taste associated with butter and celery."

Nevertheless, "it has not been generally known that lithium can lose or change taste in some patients," the case report authors wrote. Based on their findings, they suggested that in the future, taste loss or changes in taste perception should be flagged as a potential indicator of mild lithium intoxication.