This article is divided into several pages for easier reading:
- Part 01: Introduction and Defining the Terms.
- Part 02: What is Piriformis Syndrome?
- Part 03: Anatomy of the Gluteal Region.
- Part 04: What can cause Piriformis Syndrome?
- Part 05: Who can be Affected by Piriformis Syndrome?
- Part 06: Prevalence and Risk Factors.
- Part 07: What are the Symptoms?
- Part 08: How is Piriformis Syndrome Diagnosed?
- Part 09: Differential Diagnosis for Piriformis Syndrome.
- Part 10: Treatment.
- Part 11: What is the Prognosis or Outlook?
- Part 12: References and Bibliography.
9.0 Differential Diagnosis
As noted in the previous section there are a number of methods to diagnose piriformis syndrome, however, there are a variety of ailments which have similar symptoms which the reader should be aware of (Jankovic, Peng & van Zundert, 2013, p.1006; Martin et al., 2015, p.103) (not an exhaustive list):
- Sciatic neuropathy.
- Lumbar disc herniation.
- Lesion, inflammation or dysfunction of sacroiliac joint.
- Obturator internus muscle.
- Pseudoaneurysm in the inferior gluteal artery following gynaecologic surgery.
- Thrombosis of the iliac vein.
- Painful vascular compression syndrome of the sciatic nerve, caused by gluteal varicosities.
- Post-laminectomy syndrome or coccygodinia.
- Pseudoradicular S1 syndrome.
- Posterior facet syndrome at L4-5 or L5-S16.
- Unrecognised pelvic fractures.
- Lumbar osteochondrosis.
- Undiagnosed renal stones.
- Pudendal nerve entrapment.
- Ischiofemoral impingement.
- Greater trochanter ischial impingement.
- Trochanteric bursitis.
- Sacroiliac joint pain.
- Ischial tunnel syndrome.
The first four in the above list are now discussed in further detail.
9.1 Sciatic Neuropathy
Sciatic neuropathy (aka sciatica) is a painful condition that can result in chronic pain for patients, if the correct cause is not identified. Depending on the cause, sometimes known as sciatic nerve signal abnormality. Sciatic neuropathy can be caused by (not an exhaustive list) (Agnollitto et al., 2017):
- Neoplastic: of, relating to, or constituting a tumour or neoplasia.
- Compressive: In compressive sciatic neuropathy, there may be changes in the path, thickness, or signal of the sciatic nerve, with or without abnormalities of the piriformis muscle anatomy. For example, spinal radiculopathies or spinal degenerative disc disorders.
- Traumatic: Can be caused by direct trauma, pelvic ring fracture, and dislocation of the coxofemoral joint.
- Hereditary: Chief among the hereditary causes of sciatic neuropathies is Charcot-Marie-Tooth disease, which is a spectrum of diseases related to alterations currently described in more than 30 genes. In imaging studies, the finding typical of Charcot-Marie-Tooth disease is diffuse nerve hypertrophy. Clinically, patients with Charcot-Marie-Tooth disease present muscular weakness, pain, and a variety of deformities related to muscular atrophy.
- Iatrogenic: One of the main iatrogenic causes of sciatic nerve neuropathy is radiotherapy for pelvic neoplasms, including prostate, gynaecological, and colorectal cancer, resulting in radiation-induced neuropathy.
- Idiopathic: Arising spontaneously or from an obscure or unknown cause.
Other structures involved in sciatic nerve entrapment include: fibrous bands containing blood vessels, gluteal muscles, and the hamstring muscles (Martin et al, 2015).
Research suggests that piriformis syndrome has been identified to account for up to 6-8% of sciatica (Jankovic, Peng & van Zundert, 2013). Although, Zeren et al., (2015, p.987) state “The literature indicates 0.33-6% of dorsalgia and/or sciatica cases are caused by piriformis.”
9.2 Lumbar Disc Herniation
Lumbar disc herniation symptoms can appear for a variety of reasons, for example, when a person lifts something heavy and/or twists the lower back, motions that put added stress on the discs. Lumbar disc herniations are fairly common, with most often affecting people age 35 to 50.
When pressure or stress is placed on the spine, the disc’s outer ring may bulge, crack, or tear. If this occurs in the lower back (the lumbar spine), the disc protrusion may push against the nearby spinal nerve root. Or the inflammatory material from the interior may irritate the nerve. The result is shooting pains into the buttock and down the leg.
Approximately 90% of people who experience a lumbar disc herniation may have no symptoms six weeks later, even if they have had no medical treatment.
Common symptoms include:
- Leg pain is typically worse than low back pain. If the pain radiates along the path of the large sciatic nerve in the back of the leg, it is referred to as sciatica or a radiculopathy.
- The most noticeable symptoms are usually described as nerve pain in the leg, with the pain being described as searing, sharp, electric, radiating, or piercing.
- Variable location of symptoms: Depending on variables such as where the disc herniates and the degree of herniation, symptoms may be experienced in the low back, buttock, front or back of the thigh, the calf, foot and/or toes, and typically affects just one side of the body.
- Neurological symptoms: Numbness, a pins-and-needles feeling, weakness, and/or tingling may be experienced in the leg, foot, and/or toes.
9.3 Sacroiliac Joint Dysfunction
Sacroiliac joint dysfunction, also known as sacroiliac joint pain, can sometimes cause lower back and/or leg pain.
Leg pain from sacroiliac joint dysfunction can be particularly difficult to differentiate from radiating leg pain caused by a lumbar disc herniation (sciatica) as they can feel quite similar. It is estimated that the sacroiliac joint is the cause for 15-30% of lower back pain (Cohen, Chen & Neufeld, 2013).
The sacroiliac joint typically has little motion – small movements at the joint help with shock absorption and forward/backward bending. The joint is reinforced by strong ligaments surrounding it, some of which extend across the joint in the back of the pelvis. This network of soft tissues provides support, limits movement at the joint, and assists with absorbing pressure.
Other muscles that support sacroiliac joint function include the gluteus maximus and the piriformis muscle.
The primary mechanisms of sacroiliac joint dysfunction include:
- Too much movement (hypermobility or instability) in the sacroiliac joint can cause the pelvis to feel unstable and lead to pain. Pain from too much motion is typically felt in the lower back and/or hip, and may radiate into the groin area.
- Too little movement (hypomobility or fixation) can cause muscle tension, pain, and may inhibit mobility. Pain is typically felt on one side of the low back or buttocks, and can radiate down the back of leg (similar to sciatica pain).
9.4 Obturator Internus Muscle
There are a few studies that have shown that the obturator internus muscle may also potentially compress the sciatic nerve within the pelvis. Since it forms the medial border of the infrapiriform foramen, a potential site of compression, entrapment between the piriformis and obturator internus muscles could be suspected (Al-Al-Shaihk, 2015).
As noted by Benzon and colleagues (2003), individuals may have comorbid aetiologies including:
- Herniated disc;
- Failed back surgery syndrome;
- Spinal stenosis;
- Facet syndrome;
- Sacro-iliac joint dysfunction; and
- Complex regional pain syndrome.
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