Extra-spinal sciatica and sciatica mimics: a scoping review

Abstract

Not all sciatica-like manifestations are of lumbar spine origin. Some of them are caused at points along the extra-spinal course of the sciatic nerve, making diagnosis difficult for the treating physician and delaying adequate treatment. While evaluating a patient with sciatica, straightforward diagnostic conclusions are impossible without first excluding sciatica mimics. Examples of benign extra-spinal sciatica are: piriformis syndrome, walletosis, quadratus lumborum myofascial pain syndrome, cluneal nerve disorder, and osteitis condensans ilii. In some cases, extra-spinal sciatica may have a catastrophic course when the sciatic nerve is involved in cyclical sciatica, or the piriformis muscle in piriformis pyomyositis. In addition to cases of sciatica with clear spinal or extra-spinal origin, some cases can be a product of both origins; the same could be true for pseudo-sciatica or sciatica mimics, we simply don't know how prevalent extra-spinal sciatica is among total sciatica cases. As treatment regimens differ for spinal, extra-spinal sciatica, and sciatica-mimics, their precise diagnosis will help physicians to make a targeted treatment plan. As published works regarding extra-spinal sciatica and sciatica mimics include only a few case reports and case series, and systematic reviews addressing them are hardly feasible at this stage, a scoping review in the field can be an eye-opener for the scientific community to do larger-scale prospective research.

Keywords: Buttocks; Chronic Pain; Low Back Pain; Lumbar Vertebrae; Myofascial Pain Syndrome; Osteitis; Piriformis Muscle Syndrome; Sciatic Nerve; Sciatica.

Fig. 1

Schematic diagram of how to approach sciatica and sciatica mimics. LBP: low back pain, SN: sciatic nerve, H/O: history of, non-S: non specific symptoms, CBC: complete blood count, USG: ultrasonogram, R/E: routine examination, MRI: magnetic resonance imaging, CT: computed tomography, L/S: lumbar spine, SIJ: sacroiliac joint, LLD: leg length discrepancy, PR: per-rectal, N/S: nervous system, L/facet: lumbar facet, MPS: myofascial pain syndrome, GME: gluteus medius, LL: lumbar ligament, SCN: superior cluneal nerve, LCNT: lateral cutaneous nerve of thigh, SN Br.: SN branch.

Fig. 2

Imaging of piriformis muscle (PM). (A) Computed tomography based PM diameter measurement. (a), (b), and (c) represent the diameters of PM. (B) Ultrasonogram guided PM injection. Asterisks and arrow indicate hypoechoic PM and hyperechoic spinal needle trajectory, respectively. Adapted from the article of Park et al. (Korean J Pain 2011; 24: 87-92) [21] and Jeong et al. (Ultrasonography 2015; 34: 206-10) [23].

Fig. 3

Ultrasonogram of superior cluneal nerve (SCN). (A) Short axis. (B) Long axis. Yellow arrows indicate SCN. GME: gluteus medius, ES: erector spinae, GMA: gluteus maximus. Adapted from the article of Chang et al. (J Pain Res 2017; 10: 79-88) [57].

Fig. 4

Short axis ultrasonogram guided injection of lateral cutaneous nerve of thigh (LCNT). FL: fascia lata, FI: fascia iliaca, N: LCNT, SM: Sartorius muscle. Adapted from the article of Kim et al. (Korean J Pain 2011; 24: 115-8) [91].