Oral lichenoid reaction: This is a common adverse effect of various medications, including inhalers like Breztri. The reaction can manifest as red, painful papules on the tongue and other oral mucosal surfaces. The temporal relationship with starting Breztri supports this diagnosis.

Oral candidiasis: Although less directly related to Breztri, inhaled corticosteroids can increase the risk of oral candidiasis, especially if proper inhaler hygiene is not followed. Painful red papules could be part of the presentation, especially if there's an associated inflammatory response.
Nicotinic stomatitis or other irritative stomatitis: If the patient has habits that involve frequent or improper use of the inhaler, or other irritants (like tobacco), this could lead to stomatitis, presenting with red, painful lesions on the tongue and other areas of the mouth.

Aphthous ulcers: While typically found on the buccal mucosa, tongue, or floor of the mouth, aphthous ulcers can occasionally present on the back of the tongue. They are painful but usually have a more characteristic appearance (well-defined, shallow ulcers). Missing this diagnosis might not be immediately deadly, but it's crucial for appropriate management.
Oral cancer: Although rare and less likely, any new, unexplained, or persistent oral lesions should prompt consideration of oral cancer, especially in patients with risk factors (tobacco use, alcohol, etc.). Early detection is critical for prognosis.

Pemphigus vulgaris: An autoimmune disease that can cause painful blisters or erosions in the mouth, including the tongue. It's rare but should be considered if the patient has systemic symptoms or if lesions do not respond to typical treatments.
Erythema multiforme: A skin condition that can also affect the mucous membranes, including the tongue, and is characterized by target lesions. It can be triggered by medications, among other causes, and is usually self-limiting but can be severe in some cases.