def get_extended_metadata(self, item_id):
        """Get extended metadata for a media item, such as related items.

        Args:
            item_id (str): The item for which metadata is required.

        Returns:
            ~collections.OrderedDict: The item's extended metadata or None.

        See also:
            The Sonos `getExtendedMetadata API
            <http://musicpartners.sonos.com/node/128>`_
        """
        response = self.soap_client.call(
            'getExtendedMetadata',
            [('id', item_id)])
        return response.get('getExtendedMetadataResult', None)