Inflammatory low back pain Mechanical low back pain Age of onset <40 years Family history at any age Often present No past history Often present May not be present Type of onset Incognito Sudden duration of symptoms >3 months <4 weeks Nocturnal pain Often present No exercise effects Improvement Exacerbated sacroiliac joint pressure Often present No range of pain Diffuse Limited spinal mobility Loss of all planes Inability to flex and extend normally Thoracic expansion Usually reduced Normal other system involvement May present No hip involvement May present No ESR, CRP may be elevated Not elevated