A therapeutically effective amount of a histone deacetylase 6 (HDAC6) specific inhibitor compound of Formula II: or a pharmaceutically acceptable salt thereof, wherein, X is C or O; R y is independently, at each occurrence, selected from the group consisting of C 1-6 -alkyl, C 1-6 -alkoxy, halo, -C 1 - 6 haloalkyl, -C 1 - 6 dihaloalkyl, -C 1 - 6 trihaloalkyl, -OH, -N(R 1 ) 2 , -C(O)R 1 , -CO 2 R 1 , and -C(O)N(R 1 ) 2 ; or: two R y groups on the same or adjacent carbon atoms are taken together to form a C 3-8 -cycloalkyl or C 3-7 -heterocycloalkyl ring, each of which may be fused or isolated; R z is independently, at each occurrence, selected from the group consisting of C 1-6 -alkyl, C 1-6 -alkoxy, halo, -C 1 - 6 haloalkyl, -C 1 - 6 dihaloalkyl, -C 1 - 6 trihaloalkyl, -OH, -N(R 2 ) 2 , -C(O)R 2 , -CO 2 R 2 , -C(O)N(R 2 ) 2 , each R 1 is independently, at each occurrence, selected from the group consisting of H, C 1-6 -alkyl, C 3-8 -cycloalkyl, C 3-7 -heterocycloalkyl, aryl, heteroaryl, C 1-6 -alkyl-cycloalkyl, C 1-6 -alkyl-heterocycloalkyl, C 1-6 -alkyl-aryl, and C 1-6 -alkyl-heteroaryl; each R 2 is independently, at each occurrence, selected from the group consisting of H or C 1-6 -alkyl; m is 0, 1, 2, or 3; and n is 0, 1, 2, or 3; for use in treating a polycystic disease. or a pharmaceutically acceptable salt thereof, wherein, X is C or O; R y is independently, at each occurrence, selected from the group consisting of C 1-6 -alkyl, C 1-6 -alkoxy, halo, -C 1 - 6 haloalkyl, -C 1 - 6 dihaloalkyl, -C 1 - 6 trihaloalkyl, -OH, -N(R 1 ) 2 , -C(O)R 1 , -CO 2 R 1 , and -C(O)N(R 1 ) 2 ; or: two R y groups on the same or adjacent carbon atoms are taken together to form a C 3-8 -cycloalkyl or C 3-7 -heterocycloalkyl ring, each of which may be fused or isolated; R z is independently, at each occurrence, selected from the group consisting of C 1-6 -alkyl, C 1-6 -alkoxy, halo, -C 1 - 6 haloalkyl, -C 1 - 6 dihaloalkyl, -C 1 - 6 trihaloalkyl, -OH, -N(R 2 ) 2 , -C(O)R 2 , -CO 2 R 2 , -C(O)N(R 2 ) 2 , each R 1 is independently, at each occurrence, selected from the group consisting of H, C 1-6 -alkyl, C 3-8 -cycloalkyl, C 3-7 -heterocycloalkyl, aryl, heteroaryl, C 1-6 -alkyl-cycloalkyl, C 1-6 -alkyl-heterocycloalkyl, C 1-6 -alkyl-aryl, and C 1-6 -alkyl-heteroaryl; each R 2 is independently, at each occurrence, selected from the group consisting of H or C 1-6 -alkyl; m is 0, 1, 2, or 3; and n is 0, 1, 2, or 3; for use in treating a polycystic disease. two R y groups on the same or adjacent carbon atoms are taken together to form a C 3-8 -cycloalkyl or C 3-7 -heterocycloalkyl ring, each of which may be fused or isolated; R z is independently, at each occurrence, selected from the group consisting of C 1-6 -alkyl, C 1-6 -alkoxy, halo, -C 1 - 6 haloalkyl, -C 1 - 6 dihaloalkyl, -C 1 - 6 trihaloalkyl, -OH, -N(R 2 ) 2 , -C(O)R 2 , -CO 2 R 2 , -C(O)N(R 2 ) 2 , each R 1 is independently, at each occurrence, selected from the group consisting of H, C 1-6 -alkyl, C 3-8 -cycloalkyl, C 3-7 -heterocycloalkyl, aryl, heteroaryl, C 1-6 -alkyl-cycloalkyl, C 1-6 -alkyl-heterocycloalkyl, C 1-6 -alkyl-aryl, and C 1-6 -alkyl-heteroaryl; each R 2 is independently, at each occurrence, selected from the group consisting of H or C 1-6 -alkyl; m is 0, 1, 2, or 3; and n is 0, 1, 2, or 3; for use in treating a polycystic disease. <EOS>