In a 65-year-old woman who started taking telmisartan 80 mg plus hydrochlorothiazide 12.5 mg orally once daily, what is the likely cause of her diffuse burning sensation that persists all day and night?

Hydrochlorothiazide-Induced Photosensitivity is the Most Likely Cause

The burning sensation all over your patient's body is most likely due to drug-induced photosensitivity from hydrochlorothiazide, a well-documented adverse effect of thiazide diuretics that causes burning and tingling sensations in sun-exposed skin. 1

Understanding the Mechanism

Hydrochlorothiazide is a prototypical drug associated with photosensitivity reactions. Thiazide diuretics can trigger various photosensitive eruptions, including an exaggerated sunburn reaction, dermatitis, and lichenoid eruptions, with the typical presentation being a burning and tingling sensation in sun-exposed skin with associated erythema. 1 This occurs as a photo-induced cutaneous drug eruption resulting from the combination of the drug's presence in the skin and exposure to ultraviolet or visible radiation.

Clinical Presentation Details

The key features to recognize:

• Burning sensation that is persistent (all day and night in this case)
• Typically affects sun-exposed areas initially but can become generalized
• May be accompanied by erythema or rash
• Onset can occur shortly after starting the medication
• The sensation may persist even without active sun exposure once the reaction is established

Why Not Telmisartan?

While telmisartan is also listed among medications linked to photosensitivity 1, it is far less commonly implicated than hydrochlorothiazide. The FDA drug label for telmisartan does not list burning sensation or photosensitivity as common adverse effects 2. One case report exists of telmisartan aggravating pustular psoriasis 3, but this is distinct from the diffuse burning sensation described.

Immediate Management Steps

1. Discontinue hydrochlorothiazide immediately - this is the definitive treatment

2. Examine the patient for:

   • Erythema or rash on sun-exposed areas (face, neck, arms, hands)
   • Signs of more severe reactions (blistering, desquamation)
   • Systemic symptoms (fever, which would suggest a more severe hypersensitivity)

3. Switch antihypertensive regimen - Replace with an alternative that doesn't include thiazide diuretics:

   • Consider telmisartan monotherapy at higher dose (up to 80 mg) 4
   • Add a calcium channel blocker if additional BP control needed 4, 5
   • Avoid other thiazide-type diuretics (chlorthalidone, indapamide) as cross-reactivity is possible

Important Caveats

Do not confuse this with the rare but severe allergic reaction to hydrochlorothiazide that can present with septic shock-like symptoms (nausea, vomiting, fever, chest tightness, dyspnea) 6. Your patient's isolated burning sensation without systemic symptoms suggests photosensitivity rather than this severe hypersensitivity reaction.

Sun Protection Counseling

Even after discontinuing the medication, advise the patient to:

• Seek shade, especially around midday
• Wear protective clothing, broad-brimmed hats, and sunglasses
• Use broad-spectrum sunscreen with SPF ≥30 1
• Understand that radiation can be stronger when reflected by water, sand, or snow

Alternative Diagnosis Considerations

If symptoms persist after stopping hydrochlorothiazide:

• Consider small fiber neuropathy (though less likely with acute onset)
• Evaluate for other causes of dysesthesia
• Check for electrolyte abnormalities (hyponatremia from HCTZ can cause neurological symptoms, though burning sensation is atypical) 7

The resolution of symptoms within days to weeks after discontinuing hydrochlorothiazide will confirm the diagnosis. If symptoms don't improve, further neurological evaluation would be warranted.