I recently noticed a light brown stripe going down my thumbnail. Could it be a melanoma? I'm black & struggle with toenail fungus but not on my hands.

I understand your co. Your concern is valid as melanoma in blacks affects nail beds more often than in whites. But what it is too early to tell. I would advise you to look closely at the upper end of the nail fold(near the skin junction) and see if there is any growth or redness there. Also watch this streak for any changes over the next few weeks. If it changes, i.e. Becomes darker or larger, then see a dermatologist .
Nail lines. Dark lines in black people over age 20 is usually normal. Black stripes down 1 nail may be subungual hematoma. Red or brown streaks may be splinter hemorrhages. Brown/black lines from nail plate to tip are often seen in people with dark skin & are normal. Subungual Melanoma can cause nail ridges & dark colors of cuticle. It most often effects the thumbs or big toes. Dark lines may be due to othe.