Adding class to form-item
#attributes is not supported by item form elements. 


  item
  
  Description: Generate a display-only form element allowing for an optional title and description.
  
  Note: since this is a read-only field, setting the #required property will do nothing except theme the form element to look as if it were actually required (i.e. by placing a red star next to the #title).
  
  Properties: #access, #after_build, #description, #element_validate, #parents, #post_render, #prefix, #pre_render, #required, #suffix, #theme, #title, #tree, #type, #value, #weight


You would then need to add a custom theme call such as:


function MYTHEME_preprocess_form_element(&amp;$vars) {
  $vars['#attributes']['class'][] = 'another-class';
}