What causes a metallic taste in a patient with a diagnosed condition?

Metallic Taste in Diagnosed Conditions: Causes and Management

Metallic taste in patients with diagnosed conditions most commonly results from metal hypersensitivity to implants, chronic kidney disease with uremia, burning mouth syndrome, medication side effects, or systemic therapies like chemotherapy. The specific cause depends heavily on the underlying diagnosed condition and recent exposures.

Metal Hypersensitivity from Implants

If the patient has any metallic implants (orthopedic, dental, TMJ prostheses, piercings), metal hypersensitivity should be the primary consideration. 1

• Metal hypersensitivity affects 10-15% of the population and has significantly higher incidence in females. 1
• Chronic exposure to low concentrations of metal ions from dissolution, corrosion, or wear can induce hypersensitivity, with metal debris acting as haptens that trigger allergic sensitization. 1
• Symptoms range from local reactions (dermatitis, erythema) to systemic effects including neurological and gastrointestinal issues—metallic taste falls into this systemic category. 1
• Common culprit metals include Nickel (Ni), Aluminum (Al), Vanadium (V), Titanium (Ti), and Cobalt-Chromium alloys. 1

Diagnostic Approach for Metal Hypersensitivity

• Pre-implantation or current screening via skin patch tests or lymphocyte transformation tests is recommended, particularly for patients with history of intolerance to jewelry, belt buckles, or watches. 1
• The lymphocyte transformation test measures lymphocyte proliferation in presence of metal ion stimulus and can identify patients who might benefit from implant removal even when skin patch tests are negative. 1
• Contact dermatitis from nickel exposure is particularly common, and avoidance of triggering metals with topical corticosteroids hastens resolution. 1

Chronic Kidney Disease and Uremia

In patients with diagnosed chronic kidney disease (CKD) or end-stage renal disease on dialysis, metallic taste is a classic uremic symptom. 1

• Clinical manifestations of uremia include "ammonia taste and breath" as toxins accumulate in the blood. 1
• Salivary changes in CKD patients show higher concentrations of urea, creatinine, sodium, potassium, chloride, and phosphorus, which directly contribute to altered taste perception. 1
• Increased blood urea nitrogen (BUN) is responsible for high salivary pH and buffering capacity, further altering taste. 1
• Xerostomia (dry mouth) is frequent in hemodialysis patients due to reduced salivary flow, fluid restriction, and xerostomizing drugs, which compounds taste alterations. 1

Burning Mouth Syndrome (BMS)

Burning mouth syndrome commonly presents with persistently altered metallic taste or diminished taste sensations, predominantly in peri- and post-menopausal women. 1, 2

• BMS patients report both positive symptoms (burning pain, dysgeusia with metallic taste, dysesthesia) and negative symptoms (loss of taste, paresthesia) involving lips and tongue, mainly the tip and anterior two-thirds. 1, 2
• The condition is characterized by burning, stinging, or itchy sensations with mild to severe intensity, often continuous. 1
• BMS is now considered a neuropathic disorder with small fiber neuropathic changes in the tongue, showing significantly lower density of epithelial nerve fibers than controls. 2
• Quantitative sensory testing reveals significantly higher sensory thresholds in BMS patients compared to controls. 2
• Secondary causes must be excluded, including oral candidiasis, mucosal lesions, hematological disorders, autoimmune disorders, and pharmacological side effects. 1

Management of BMS

• Reassurance and education are crucial, as patients can be told the condition will not worsen, which is often therapeutic in itself. 1
• Treatment is primarily via medications that suppress neurologic transduction and transmission (neuropathic pain medications). 1, 2
• Cognitive behavioral therapy (CBT) is recommended. 1
• Current treatments are palliative only, with few studies showing relief significantly better than placebo. 2

Medication and Systemic Therapy Side Effects

Metallic taste is a well-documented side effect of numerous medications and cancer treatments. 3, 4

• In cancer patients receiving systemic therapy, 46% report taste changes, with 34% of those experiencing metallic taste specifically. 3
• Patients treated with chemotherapy, concomitant radiotherapy, and targeted therapy are all at risk, with women experiencing metallic taste more often than men. 3
• Patients with metallic taste also more frequently report being bothered by sour food and that everything tastes bitter. 3
• Metallic taste has been reported with botulinum toxin A administration, though it is self-limited and diminishes with successive treatments. 4
• Alteration in zinc metabolism has been suggested as a possible mechanism for medication-induced metallic taste. 4

Olfactory and Taste Disorders

Post-viral olfactory loss, including from COVID-19, can present with taste disturbances including metallic taste. 5, 6

• Post-viral olfactory loss accounts for 20-25% of specialist clinic presentations with chemosensory disturbances. 5, 6
• COVID-19 causes chemosensory dysfunction in 59-86% of patients, with recovery occurring in 44-73% within the first month, though some develop persistent dysfunction. 5
• Objective psychophysical testing using validated instruments (UPSIT or Sniffin'Sticks) combined with rigid nasal endoscopy is recommended to differentiate between conductive and sensorineural causes. 5
• Phantosmia (olfactory hallucinations) can occur from viral infections, head trauma, sinonasal inflammatory disease, tumors, or neurodegenerative diseases. 6

Rare but Important Causes

• Foreign bodies containing copper or other metals in the gastrointestinal tract can cause chronic metallic taste through copper overload. 7
• In one case, endoscopic removal of a copper-containing foreign body from the gastric wall resolved chronic metallic taste after serum copper levels were found elevated. 7

Diagnostic Algorithm

1. Obtain detailed history focusing on:

   • Presence of any metallic implants (orthopedic, dental, TMJ, piercings)
   • Diagnosed chronic kidney disease or dialysis status
   • Current medications and cancer treatments
   • Recent viral infections or COVID-19
   • History of metal intolerance (jewelry, watches, belt buckles)
   • Timing of onset relative to any procedures or exposures

2. Physical examination should include:

   • Nasal endoscopy to identify sinonasal pathology 5, 6
   • Oral examination for mucosal lesions, gingivitis, or signs of BMS 1, 2
   • Neurological examination focusing on cranial nerves 6

3. Laboratory testing based on suspected etiology:

   • Serum creatinine, BUN, and electrolytes if CKD suspected 1
   • Serum copper levels if foreign body suspected 7
   • Hematological screening to exclude secondary causes of BMS 1

4. Specialized testing when indicated:

   • Skin patch tests or lymphocyte transformation tests for metal hypersensitivity 1
   • Objective olfactory testing (UPSIT or Sniffin'Sticks) for chemosensory dysfunction 5, 6
   • MRI orbits, face, and neck if imaging needed for olfactory apparatus 6

5. Treatment directed at underlying cause:

   • Metal hypersensitivity: Consider implant removal or replacement with alternative materials (e.g., all-titanium alloy) 1
   • CKD/uremia: Optimize dialysis and manage uremic symptoms 1
   • BMS: Neuropathic pain medications, CBT, reassurance 1, 2
   • Medication-related: Consider alternative medications if possible 3, 4
   • Post-viral: Olfactory training for minimum 3-6 months 5