Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Call emergency services for trouble breathing, swelling of the face or tongue, faintness, or a widespread blistering or peeling rash after using a medicine.
These may be signs of a serious treatment reaction rather than familial lichen amyloidosis itself.
Seek prompt medical care for rapidly spreading redness, increasing warmth or pain, pus, red streaks, or fever.
These may indicate an infection where scratching has broken the skin.
Arrange a routine medical appointment for persistent itchy bumps, especially if close relatives have similar skin changes.
Seek assessment if a known patch spreads, itching regularly disrupts sleep, or treatment no longer controls symptoms.
The article also says
Contact the clinician managing your treatment if you notice skin thinning, easy bruising, severe irritation, or other possible side effects.
New or changing lesions may need examination or another biopsy.
Every sign above is quoted from the sofidex article on Familial lichen amyloidosis. If you are not sure, err upward — it is always reasonable to be checked.