뿸 03312, 가톨릭대학교 의과대학 은평성모병원 재활 의학교실

https://doi.org/10.35827/cp.2021.20.1.43

접수일 : 2020 년 10 월 20 일 , 게재승인일 : 2020 년 11 월 24 일 책임저자 : 박지혜 , 서울시 은평구 통일로 1021

뿸 03312, 가톨릭대학교 의과대학 은평성모병원 재활 의학교실

Tel: 02-2030-4619, Fax: 02-2030-4620 E-mail: [email protected]

신경과 먼 부위 근육 내 주사 후 발생한 좌골신경병증

가톨릭대학교 의과대학 은평성모병원 재활의학교실

윤수인ㆍ박지수ㆍ고윤담ㆍ송대헌ㆍ박지혜

Sciatic Neuropathy after Intramuscular Injection at a Site Remote from the Nerve

Soo In Yun, M.D., Jisoo Park, M.D., Yun Dam Ko, M.D., Dae-Heon Song, M.D., Ph.D. and Jihye Park, M.D.

Department of Rehabilitation Medicine, Eunpyeong St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea

Sciatic nerve can be injured by various mechanism such as compression, traction during surgery, and direct trauma. This case reports a sciatic neuropathy caused by compression due to hematoma occurring after intramuscular injection in the gluteus medius muscle far from the nerve. In order to avoid occurrence of sciatic neuropathy after buttock injection, the injection was made in the upper outer quadrant of the buttock, but sciatic neuropathy occurred. Sciatic neuropathy can be confused with lumbar radiculopathy, so differential diagnosis is important. (Clinical Pain 2021;20:43-48)

Key Words: Sciatic neuropathy, Intramuscular injection, Gluteus medius

INTRODUCTION

The sciatic nerve originates from the L4-S3 nerve roots, the anterior division becomes the tibial nerve and the poste- rior division becomes the common peroneal nerve. The sci- atic nerve exits the pelvis through the greater sciatic fora- men and passes beneath the piriformis muscle. The sciatic nerve, covered by the gluteus maximus, then runs medial and posterior to the hip joint. It supplies sensation to the distal leg except for the medial area and foot, and in- nervates the muscles of the anterior/lateral and posterior compartments of the legs. These muscles function as knee flexion, ankle dorsiflexion, and ankle plantar flexion.

Nerve injury after injection is relatively common and the sciatic nerve is one of the most commonly involved nerves.

The causes of sciatic neuropathy include direct trauma, per- ineural nerve injection injury, infarction, or compression [1].

In this case report, we present a case of sciatic neuro-

pathy caused by hematoma after intramuscular injection of the gluteus medius muscle, a remote site from the sciatic nerve.

CASE REPORT

A 68-year-old man visited to neurosurgery outpatient

clinic with severe pain in the left gluteal area which radi-

ated down the calf for a week. He had chronic lower leg

pain, but recently complained that the pain has worsened

and cannot walk. There was no specific history of trauma

to the area. There was no underlying disease other than dia-

betes mellitus, and he was taking diabetes and pain

medication. Lumbar X-ray showed degenerative spondy-

losis, and lumbar spine computed tomography (CT) and

magnetic resonance imaging (MRI) were performed with

suspicion of lumbosacral radiculopathy, but there were no

abnormalities. Thus he was prescribed pain medications

and planned a follow-up visit. The patient returned 2 weeks

later with aggravated pain and was hospitalized for further

evaluation and treatment. In the last two weeks, he was

given several blocks at his lower back and an intramuscular

injection in the left buttock, especially in the upper outer

quadrant of gluteus medius at the local pain clinic. On

physical examination, manual muscle tests revealed weak-

ness of left toe and ankle dorsiflexion, which was grade

Table 1. Sensory Nerve Conduction Study

Sensory nerve Stimulation Peak latency (ms) Amplitude (μV) Distance (cm) CV (m/s)

Rt. Sural Calf 3.8 10.4 14.0 44

Lt. Sural Calf 3.9 10.0 14.0 44

Rt. Superficial peroneal Lower leg 2.8 12.4 9.0 41

Lt. Superficial peroneal Lower leg 3.1 7.0* 9.0 39

Rt.: Right, Lt.: Left, ms: millisecond, μV: microvolt, CV: conduction velocity, m/s: meter/second.

*Decreased amplitude of SNAP.

Table 2. Motor Nerve Conduction Study

Motor nerve Stimulation Onset latency (ms) Amplitude (mV) Distance (cm) CV (m/s)

Rt. Peroneal (EDB) Ankle 4.9 0.3 29.0 38

B.Fib 12.5 0.2

Lt. Peroneal (EDB) Ankle 5.0 0.1* 29.0 28

B.Fib 15.3 0.1

Rt. Peroneal (TA) Fib Head 2.6 4.8 6.0 60

Poplit 3.6 4.7

Lt. Peroneal (TA) Fib Head 4.1 1.1* 6.0 50

Poplit 5.3 1.1

Rt. Tibial (AH) Ankle 3.8 12.8 36.0 43

Poplit 12.1 8.5

Lt. Tibial (AH) Ankle 3.7 12.8 37.0 41

Poplit 12.8 7.9

Rt.: Right, Lt.: Left, EDB: Extensor digitorum brevis, TA: Tibialis anterior, AH: Abductor hallucis, B.Fib: Below fibular head, Fib Head: Fibular head, Poplit: Popliteal fossa, ms: millisecond, mV: millivolt, CV: conduction velocity, m/s: meter/second.

*Decreased amplitude of CMAP.

2 according to the Medical Research Council (MRC) scale for muscle strength. The paresthesia and hypesthesia was localized in left lateral calf and foot dorsum. Pathologic re- flexes were negative and deep tendon reflexes of knee and ankle were normoactive. There was tenderness in the left lateral mid-buttock area. In blood test, C-Reactive Protein showed a mild elevation of 1.30 mg/dl (normal range: 0.01∼

0.5 mg/dl), and other abnormalities were not observed.

Because lumbar spine imaging studies did not show specif- ic findings to demonstrate the symptoms, electrodiagnostic study was requested. Nerve conduction study of lower ex- tremity showed reduced amplitude of sensory nerve action potential (SNAP) in left superficial peroneal nerve and re- duced amplitude of compound muscle action potential (CMAP) in left common peroneal nerve recording at ex- tensor digitorum brevis muscle. The conduction velocity of

CMAP around fibular neck was normal (Table 1, 2). On

needle electromyography (EMG), left L4-L5 paraspinalis,

gluteus medius, tibialis anterior, and peroneus longus

showed positive sharp waves (Table 3). Base on the results,

we suggested a left peroneal neuropathy combined with left

superior gluteal neuropathy, but it is uncommon for the two

distant nerves to be involved. Therefore, we recommended

the pelvis MRI to demonstrate the lesion that causes

neuropathies. In the pelvis MRI, 6 × 6 × 2.4 cm sized het-

erogenous mass-like lesion was found within the left glu-

teal medius muscle, which was probably intramuscular

hematoma (Fig. 1, 2), and the distal portion of the hema-

toma was close to the lateral side and above of the sciatic

nerve (Fig. 1-B, 2-B, C). Furthermore, there was partial

tear of left gluteus maximus and gluteus medius muscles

(Fig. 2). There was no definite signal intensity change or

Table 3. Needle Electromyography

Muscle IA Fib PSW MUAP Recruitment pattern Interferential pattern

Both L2-L4 paraspinalis NL None None

Rt. L4-L5 paraspinalis NL None None

Lt. L4-L5 paraspinalis NL None 1＋

Both L5-S1 paraspinalis NL None None

Both Gluteus Maximus NL None None NL NL Full

Both Tensor Fascia Lata NL None None NL NL Full

Both Gastrocnemius (med) NL None None NL NL Full

Both Soleus NL None None NL NL Full

Lt. Gluteus Medius NL None 2＋

NL NL Reduced

Lt. Vastus Medialis NL None None NL NL Full

Lt. Tibialis Anterior NL None 2＋

NL NL Discrete

Lt. Tibialis Posterior Increased* None None NL NL Full

Lt. Peroneus Longus NL None 2＋

NL NL Discrete

Rt. Tibialis Anterior NL None None NL NL Full

Rt. Peroneus Longus NL None None NL NL Full

IA: insertional activity, Fib: Fibrillation, PSW: Positive sharp wave, MUAP: Motor Unit Action Potential, NL: Normal, Poly:

Polyphasic.

*Increased insertional activities at rest.

†

Abnormal spontaneous activities at rest.

‡

Discrete to reduced interferential patterns on maximal volition.

Fig. 1. Axial T2-weighted pelvis magnetic resonance imaging. (A) In proximal section, intramuscular hematoma (void arrow) with de- creased signal intensity was seen in left gluteal medius muscle. (B) In distal section, distal portion of hematoma (arrow) of left gluteal medius muscle was located ad- jacent to left sciatic nerve (arrow head).

swelling of the sciatic nerve. Based on the results of elec- trodiagnostic study and imaging studies, we concluded that the causative lesion was sciatic neuropathy, especially in- volving the peroneal division, due to the hematoma in the gluteus medius muscle. The patient was given sciatic and superficial peroneal nerve block for pain control. Pain in the left gluteal area and paresthesia in the calf area im- proved, but left foot drop did not show much improvement when followed for more than 10 months.

DISCUSSION

The sciatic nerve is the widest and longest nerve, and at the distal it is divided into the tibial and the common peroneal nerve. One of the most common symptoms of sci- atic neuropathy is foot drop. Weakness of knee flexion and a decrease in the ankle reflex may occur, in addition to this, radiating pain in the lower extremities and loss of sensation in the foot may occur [2]. Similar symptoms can occur in lumbar radiculopathy, but treatment approaches are different.

Therefore, it is important to differentiate between sciatic

neuropathy and lumbosacral radiculopathy.

Fig. 2. Sagittal and coronal T2-weighted pelvis magnetic resonance imaging. (A) In sagittal view, intramuscular hematoma in gluteus medius (void arrow) with decreased signal intensity and partial tear in left gluteus maximus (open white arrow) with increased signal intensity were seen. (B) In sagittal view, the proximal (void arrow) and distal portion (white arrow) of the hematoma were seen separately. Distal portion of the hematoma (white arrow) was located adjacent to sciatic nerve (arrow head). (C) In coronal view, partial tear in left gluteus medius (black arrow) with increased signal intensity was observed. Distal portion of the hematoma (white arrow) was located above the sciatic nerve (arrow head).

The sciatic nerve has a long course and is susceptible to damage. Sciatic neuropathy can be caused by various mechanisms such as hip replacement, acute external com- pression, nerve infarction, hip dislocation, femur fracture, contusion, and gluteal injection [3]. Among several etiol- ogies of sciatic neuropathy, intramuscular injection ac- counts for 2.7%, and 20% of all injection-related peripheral nerve damage occurs in the gluteal region [3,4]. Gluteus maximus and gluteus medius muscles are preferred for in- tramuscular injection because of their large size and fewer blood vessels and nerves. To prevent damage to the sciatic nerve, it is recommended to inject into the upper outer quadrant.

The postulated mechanisms of sciatic neuropathy after intramuscular injection of gluteal area can be divided into direct needle damage, direct nerve damage by neurotoxic agents, secondary constriction by scar, ischemia, and com- pressive damage caused by hematoma. The length of the needle and the position and angle of the needle during in- jection are related to direct needle injury [1,5]. There are several case reports of compressive sciatic neuropathy caused by gluteal hematoma, which was caused by trauma, surgery, and inferior gluteal artery rupture by trauma [3,6-8]. In these cases, a hematoma near the sciatic nerve directly caused compression, or a hematoma was large enough to cause compartment syndrome. Most cases did

not clearly describe which gluteal muscle hematoma devel- oped, but one case described that hematoma occurred in gluteus maximus [8]. But in this case, the main mechanism of sciatic neuropathy seems to be compression caused by hematoma in gluteus medius despite injection in the upper outer quadrant. Gluteus medius is located superior to pir- iformis and is far from the sciatic nerve. Sciatic neuropathy caused by lesion in gluteus medius has not been reported yet.

There are two considerations as to the hematoma causing sciatic neuropathy. The first is the reason for the occur- rence of the hematoma, and the second is how the hema- toma in gluteus medius muscle affected the sciatic nerve.

The first hypothesis that hematoma has occurred is high bleeding tendency. The risk factors for hematoma include coagulation disorder, renal, cardiac, hepatic insufficiency, and anticoagulant therapy. This patient had diabetes melli- tus as underlying disease, but blood tests showed no evi- dence of coagulation disease, renal disease, or hepatic dis- ease and he did not receive anticoagulant therapy. Among the medications taken by the patient, glimepiride is a drug that can cause thrombocytopenia, but it was not observed in the laboratory test performed at hospitalization.

Therefore, we concluded that the patient did not have a

high tendency to bleed. The second hypothesis is superior

gluteal artery rupture by injection. Superior gluteal artery

is the largest branch originating from the internal iliac ar- tery and exiting the pelvis via the greater sciatic foramen, superior the piriformis muscle. It gives off superficial and deep branches. The superficial branch travels between sur- face of gluteus medius and deep surface of gluteus max- imus, and the deep branch travels to the deep surface of gluteus medius. The upper outer quadrant is close to these structures, so if the injection is done too low or medial in the upper outer quadrant, superior gluteal artery can be damaged [7].

The first hypothesis that the hematoma of gluteus med- ius muscle caused sciatic neuropathy is the anatomical var- iants of the sciatic nerve. According to Beaton and Anson classification, there are six types of anatomical variants for the sciatic nerve, and type 3, 5 and 6 are more likely to be affected by lesions of the gluteus medius muscle be- cause the sciatic nerve is located above the piriformis muscle. However, in this case, pelvis MRI findings showed that the sciatic nerve was type 1, passing under the piriformis. Thus, it is unlikely that this hypothesis is the cause of sciatic neuropathy. Another hypothesis is gluteal compartment syndrome. If hemorrhage is large, gluteal compartment syndrome can cause sciatic neuropathy [9]. In compartment syndrome, an infiltrative or feather-like pat- tern of hyperintensity is observed in the MR T2-weighted image, meaning muscle compartment edema. In addition, a change in muscle signal intensity can be observed due to muscle ischemia. These findings were not observed in this case, and it is less likely. On MRI of this case, a hema- toma was observed adjacent to the sciatic nerve, and it is presumed that the intramuscular hemorrhage moved down- ward and pressed the sciatic nerve.

This case was diagnosed with the sciatic neuropathy mainly involving in peroneal division caused by gluteal hematoma around the sciatic nerve which occurred after injection. There was a limitation in the electrodiagnostic study. In order to differentiate between sciatic neuropathy and peroneal neuropathy, it is necessary to perform needle EMG on proximal muscles such as biceps femoris short head innervated by the sciatic nerve. Because the muscles were not examined, it was difficult to differentiate.

However, there was no decrease in conduction velocity of CMAP around the fibular head, where peroneal neuropathy commonly occured, and hematoma was found in gluteus medius on pelvis MRI. Comprehensive interpretation of

electrodiagnostic study and imaging studies led to a con- clusion that was sciatic neuropathy especially involving the peroneal division. The sciatic nerve consists of peroneal and tibial divisions. Considering the anatomical structure of the sciatic nerve that the peroneal fascicle is located on the lateral side, it is likely that only the peroneal division close to the hematoma was injured. In addition, peroneal division has a larger fascicle and less supportive connective tissue compared to tibial division, so it is more vulnerable to in- jury [10].

It is known that sciatic nerve injury remains as a sequela such as paresthesia and weakness of the leg. In one study, significant sequelae remained in two thirds of patients who developed sciatic neuropathy by intramuscular injection [4].

In another study, regardless of cause, 75% of sciatic neuro- pathy patients showed improvement with partial recovery at a 3-year long-term follow-up. This study also revealed the CMAP amplitude of extensor digitorum brevis muscle and the degree of paralysis of ankle plantar and dorsi- flexion as prognostic factors. If the CMAP is not measured or the degree of weakness is severe, the prognosis is poor [3]. In our case, the CMAP amplitude of the extensor dig- itorum brevis muscle, but the affected side was more se- verely reduced by one third compared to the unaffected side. The muscle strength of the ankle dorsiflexor was se- verely reduced to grade 2. This patient is likely to have a poor prognosis.

Treatment depends on the cause. If compression or com- partment syndrome is the cause, surgical exploration and decompression are required. Ankle-foot orthosis is helpful for foot drop due to severe weakness, and medications for neuropathic pain such as nortriptyline, gabapentin, carba- mazepine, and mexilitine can be used as symptomatic treat- ment for dysesthesia. Nerve block is also useful for dyses- thesia [10]. In our case, sciatic nerve, superficial peroneal nerve, and piriformis muscle blocks were performed for pain, and the pain gradually improved. Decompression was not performed because it was hematoma, not compartment syndrome, and muscle weakness is under follow-up.

In conclusion, even if an injection is given away from

the nerve, compressive sciatic neuropathy due to an intra-

muscular hematoma can occur. It is necessary to dis-

tinguish it from lumbosacral radiculopathy because it dif-

fers in treatment. Sciatic neuropathy can leave sequelae, so

care should be taken even if an injection is made into the

gluteal muscles remote from the sciatic nerve.

CONFLICT OF INTEREST

The authors declare that there are no conflicts of interest to disclose. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

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