UILabel在长文本的顶部和底部显示更多空白区域

我想在滚动视图中显示属性文本标签。我使用以下代码标签显示中间的文本，并在顶部和底部添加一些额外的空白区域。下面UILabel在长文本的顶部和底部显示更多空白区域

NSString *STR_titl_iten_des = @"Item Description"; 
    NSString *STR_descrip_detail = @"Long text to be displayed"; 

    self.lbl_item_descrip.numberOfLines = 0; 
    NSString *text2 = [NSString stringWithFormat:@"%@\n%@",STR_titl_iten_des,STR_descrip_detail]; 

    if ([self.lbl_item_descrip respondsToSelector:@selector(setAttributedText:)]) { 
     NSDictionary *attribs = @{ 
            NSForegroundColorAttributeName: self.lbl_item_descrip.textColor, 
            NSFontAttributeName: self.lbl_item_descrip.font 
            }; 
     NSMutableAttributedString *attributedText = 
     [[NSMutableAttributedString alloc] initWithString:text2 
               attributes:attribs]; 
     NSRange cmp = [text2 rangeOfString:STR_titl_iten_des]; 
     if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad) 
     { 
      [attributedText setAttributes:@{NSFontAttributeName:[UIFont fontWithName:@"HelveticaNeue-Bold" size:21.0]} 
            range:cmp]; 
     } 
     else 
     { 
      [attributedText setAttributes:@{NSFontAttributeName:[UIFont fontWithName:@"HelveticaNeue-Bold" size:17.0]} 
            range:cmp]; 
     } 
     self.lbl_item_descrip.attributedText = attributedText; 

    } 
    else 
    { 
     self.lbl_item_descrip.text = text; 
    } 

    [_lbl_item_descrip sizeToFit];

是我的输出