TT #122 · Parshas Tazria · Aliyah 2 · Passuk 10
English: If the eruption spreads out in the skin, so that the eruption covers all the skin of the affected person from head to foot, as far as the priest can see,
Chabad.org — Chumash, English translation + Rashi for Vayikra 13:12
Torah Temimah cites Sifra (Toras Kohanim) for spreading from either the lower body upward or the upper body downward.
Sifra — Vayikra 13, Midrash Sefer
English: The rule applies whether the eruption spreads from below upward or from above downward.
Textual derivation
The direction of spread does not change the rule: spread from below upward and from above downward are both included.