If the pain relates to the coccyx, this should produce immediate relief.If the anesthetic test proves positive, then a dynamic (sit/stand) x-ray or MRI scan may show whether the coccyx dislocates when the patient sits.Use of dynamic x-rays on 208 patients who gave positive results with the anesthetic test showed:

31% Not possible to identify the cause of pain
27% Hypermobility (excessive flexing of the coccyx forwards and upwards when sitting)
22% Posterior luxation (partial dislocation of the coccyx backwards when sitting)
14% Spicule (bony spur) on the coccyx
5%  Anterior luxation (partial dislocation of the coccyx forwards when sitting)This study found that the pattern of lesions was different depending on the obesity of the patients: obese patients were most likely to have posterior luxation of the coccyx, while thin patients were most likely to have coccygeal spicules. Angle of incidence
Sagittal coccygeal movement is measured using the angle of incidence—or the angle at which the coccyx strikes the seat when an individual sits down. A smaller angle indicates the coccyx being more parallel to the seat, resulting in flexion (or “normal” movement) of the coccyx. A larger angle indicates the coccyx being more perpendicular to the seat, causing posterior subluxation (or “backward” movement) of the coccyx. Causes
One way of classifying coccydynia is whether the onset was traumatic versus non-traumatic. In many cases the exact cause is unknown and is referred to as idiopathic coccydynia. Coccydynia is a fairly common injury which can often result from falls, particularly in leisure activities such as cycling and skateboarding.
Indian childhood cirrhosis is a chronic liver disease of childhood characterised by cirrhosis of the liver associated with the deposition of copper in the liver. It primarily affects children of 1–3 years of age and has a genetic predisposition. It had a very high case fatality in the past, but has eventually become preventable, treatable and is now rare.It remains a part of the differential diagnosis of Wilsons disease. See also
North American Indian childhood cirrhosis

References
Further reading

Nayak N.C.; Chitale A.R. (2013). "Indian childhood cirrhosis (ICC) & ICC-like diseases: The changing scenario of facts versus notions". Indian J. Med. Res. 137 (6): 1029–42. PMC 3734708. PMID 23852284.