Catalysis of the reaction: cis-1,2-dihydroxy-4-methylcyclohexa-3,5-diene-1-carboxylate + NADP+ = 4-methylcatechol + NADPH + H+ + CO2.
cis-1,2-dihydroxy-4-methylcyclohexa-3,5-diene-1-carboxylate:NAD(P)+ oxidoreductase (decarboxylating)