“Small brownish spot on arm not going away?”
Female | 46 years old
Complaint duration: 2 months
Medications: Tizanidine, Bupropin, Gabapentin, Diclofenic
Conditions: Fibromyalgia, Psoriasis, Eczema, Possible PsA

3 Answers
DermatologyDermapathologistAge spots: These are common and usually harmless, caused by sun exposure over time.
Mole or freckle: It might be a mole or freckle that has changed.
Skin irritation: Your psoriasis or eczema could cause changes in your skin.
Other issues: Sometimes, spots that don't heal or grow might need to be checked for more serious problems.
Since the spot has been there for two months and is getting bigger, it's a good idea to see a doctor. Contact Irvine Skin for a professional checkup to be safe.
https://irvineskin.com/inquiry-now/
The pic does not define it as well as an exam would but one strong possibility - fitting with your initial assumption- is a consequence of a bruise: telangiectasias (little spider veins) & hyperpigmentation (brown spot) from iron in blood. Best is to see a board certified dermatologist.