  We present new spectroscopic and polarimetric observations of the
gravitational lens SDSS J1004+4112 taken with the 6m telescope of the Special
Astrophysical Observatory (SAO, Russia). In order to explain the variability
that is observed only in the blue wing of the C IV emission line, corresponding
to image A, we analyze the spectroscopy and polarimetry of the four images of
the lensed system. Spectra of the four images were taken in 2007, 2008, and
2018, and polarization was measured in the period 2014-2017. Additionally, we
modeled the microlensing effect in the polarized light, assuming that the
source of polarization is the equatorial scattering in the inner part of the
torus. We find that a blue enhancement in the CIV line wings affects component
A in all three epochs. We also find that the UV continuum of component D was
amplified in the period 2007-2008, and that the red wings of CIII] and CIV
appear brighter in D than in the other three components. We report significant
changes in the polarization parameters of image D, which can be explained by
microlensing.Our simulations of microlensing of an equatorial scattering region
in the dusty torus can qualitatively explain the observed changes in the
polarization degree and angle of image D. We do not detect significant
variability in the polarization parameters of the other images (A, B, and C),
although the averaged values of the polarization degree and angle are different
for the different images. Microlensing of a broad line region model including a
compact outflowing component can qualitatively explain the CIV blue wing
enhancement (and variation) in component A. However, to confirmed this
hypothesis, we need additional spectroscopic observation in future.
