Piriformis syndrome

Piriformis syndrome
Location of piriformis syndrome within the body
Classification and external resources
Specialty	Orthopedics, sports medicine
ICD-10	G57.0
ICD-9-CM	355.0
eMedicine	article/87545
MeSH	D055958
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Piriformis syndrome is a somewhat controversial diagnosis of a neuromuscular disorder which is related to the sciatic nerve. According to the terms of the syndrome, the sciatic nerve becomes compressed or otherwise irritated by the piriformis muscle causing pain, tingling and numbness in the hip/ buttocks and along the path of the sciatic nerve descending the lower thigh and into the leg. It is one of the few conditions which causes posterior hip pain. The condition has no external signs. Diagnosis is often difficult due to few validated and standardized diagnostic tests, but two tests have been well-described and clinically validated: one is electrophysiological, called the FAIR-test, which measures delay in sciatic nerve conductions when the piriformis muscle is stretched against it. The other is magnetic resonance neurography, a type of MRI that highlights inflammation and the nerves themselves. Some say that the most important criterion is the exclusion of sciatica resulting from compression/irritation of spinal nerve roots, as by a herniated disc. However, compression may be present, but not causal, in the setting of sciatica due to piriformis syndrome. Recovery time ranges between a few days to six weeks or more for complete recovery.

Possible causes of the syndrome are anatomical variations in the muscle-nerve relationship in the hip which place the piriformis muscle too close to the sciatic nerve (cadaver studies have shown this condition to be rather rare, however), or from simple overuse or strain that causes swelling in the muscle and compression on the nerve. Other research has suggested that pinching of the S1 nerve around the spine may cause the piriformis muscle to spasm secondarily; regardless, pain in the area of the piriformis often co-occurs with bona fide sciatica.

One large scale formal prospective outcome trial found that the weight of the evidence-based medicine is that piriformis syndrome should be considered as a possible diagnosis when sciatica occurs without a clear spinal cause. The need for controlled studies is supported by studies of spinal disc disease that show a high frequency of abnormal discs in asymptomatic patients. Although damage to lower spinal discs is frequently associated with sciatic pain, such pain itself is not consistently associated with damaged discs, meaning other reasons (such as the swelling of the piriformis muscle) need to be considered, though spasms of the piriformis may also be caused by damage to the nerve roots of the sacrum— the causal relationship remains unclear, and the existence of the syndrome is itself open to question.

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