  Little Strings are a type of non-gravitational quantum theories that contain
extended degrees of freedom, but behave like ordinary Quantum Field Theories at
low energies. A particular class of such theories in six dimensions is
engineered as the world-volume theory of an M5-brane on a circle that probes a
transverse orbifold geometry. Its low energy limit is a supersymmetric gauge
theory that is described by a quiver in the shape of the Dynkin diagram of the
affine extension of an ADE-group. While the so-called $\widehat{A}$-type Little
String Theories (LSTs) are very well studied, much less is known about the
$\widehat{D}$-type, where for example the Seiberg-Witten curve (SWC) is only
known in the case of the $\widehat{D}_4$ theory. In this work, we provide a
general construction of this curve for arbitrary $\widehat{D}_{M}$ that
respects all symmetries and dualities of the LST and is compatible with
lower-dimensional results in the literature. For $M=4$ our construction
reproduces the same curve as previously obtained by other methods. The form in
which we cast the SWC for generic $\widehat{D}_M$ allows to study the behaviour
of the LST under modular transformations and provides insights into a dual
formulation as a circular quiver gauge theory with nodes of $Sp(M-4)$ and
$SO(2M)$.
