근막통증후군으로 오인된 신경초종

VOL. 13, NO. 1, 2014

CLINICAL PAIN 33 접수일 _{: 2014} 년 ₃ 월 ₄ 일 _, 게재승인일 _{: 2014} 년 ₅ 월 ₂₈ 일

책임저자 _: 장원혁 _, 서울시 강남구 일원동 ₅₀

󰂕 _135-710, 성균관대학교 의과대학 삼성서울병원 재

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근막통증후군으로 오인된 신경초종

󰠏 증례 보고 󰠏

성균관대학교 의과대학 삼성서울병원 재활의학교실,

신경외과교실

김강희

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Schwannoma Misconceived as Myofascial Pain Syndrome

󰠏 A Case Report 󰠏

Kang Hee Kim, M.D.

, Sun-Ho Lee, M.D., Ph.D.

, Kyeong Eun Uhm, M.D.

, Jaechan Park, M.D.

and Won Hyuk Chang, M.D., Ph.D.

Departments of

Physical and Rehabilitation Medicine,

2

Neurosurgery, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea

We herein reported a case of schwannoma misdiagnosed as myofascial pain syndrome for a long time. A 36 years old male patient visited our hospital for proper management for an intermittent left inter-scapular area pain radiating to the posterolateral thoracic area. He was diagnosed with my- ofascial pain syndrome because of the characteristics of a tender point and referred pain on visits to several clinics.

On physical examination, a mass was palpated at the left middle para-thoracic muscle. A thoracic spine Magnetic res- onance imaging revealed an oval shaped mass in the left erector spinae muscle. It was suspected to be a schwanno- ma and the patient underwent tumor removal. After excision of the schwannoma, the symptoms were completely all- eviated. If a case of suspected myofascial pain syndrome does not fulfill the criteria or does not improve on con- servative treatment, the physician should consider other eti- ologies and perform imaging studies for accurate diagnosis.

(Clinical Pain 2014;13:33-36)

Key Words: Myofascial pain syndrome, Schwannoma, MRI

INTRODUCTION

Myofascial pain syndrome (MPS) is the most frequent pain conditions encountered in the general population. A report from an internal medicine group practice reported that 30% of patients with a pain complaint had active my- ofascial trigger points (MTrPs).

For the clinical diagnosis of MPS, it is essential to apply accurate diagnostic criteria that reliably distinguish MTrPs from other pain syndromes.

The widely accepted MPS description by Travell and Simon

stipulates that it is a disorder characterized by acute or chronic nonspecific pain that affects a small number of muscles, and involves single or multiple MTrPs that usu- ally are located within affected muscles or fascia. MTrPs can give rise to characteristic referred pain, motor dysfunc- tion, and autonomic phenomena which are the most im- portant diagnostic clues in MPS.

The three most important criteria for the diagnosis of MTrPs were spot tenderness, taut band, and pain recognition.

Referred pain and local twitch response (LTR) can be confirmatory signs of MTrPs.

Because trigger point injection is effective therapy and can elicit LTR more easily, trigger point injection is widely used for treatment, as well as diagnosis of MPS.

MPS have been described as a commonly overlooked

source of musculoskeletal pain.

However, MPS remains

controversial because there are no objective laboratory

tests.

In addition, previous studies for diagnostic reliability

showed inconsistent results.

These reasons could lead to

the overdiagnosis or misdiagnosis of MPS for several dif-

ferent presentations of musculoskeletal pain.

In this manu-

script, we reported a case of schwannoma misdiagnosed as

myofascial pain syndrome for a prolonged period. The fol-

lowing report demonstrated the importance of applying ac-

curate diagnostic criteria of MPS.

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CLINICAL PAIN 34

Fig. 1. Thoracic spine Magnetic Resonance Imaging showed a 1.5×1.2×2.1 cm sized oval shaped mass in the left erector spinae muscle at the T8∼T9 level. (A) Iso-signal intensity in T1 weighted imaging. (B) High-signal intensity in T2 weighted imaging. (C) Enhanced in contrast-using imaging.

Fig. 2. Gross findings of the mass.

CASE REPORT

A 36-yr-old male patient with no relevant or significant medical history presented with intermittent left inter-scap- ular area pain radiating to left the posterolateral thoracic area. This symptom developed abruptly after weight train- ing exercise 3 years prior. The pain worsened with sitting posture, however, the pain was continuous with no relief.

The pain was not associated with any progressive neuro- logic symptoms or signs. The patient was diagnosed with myofascial pain syndrome because of the character of a tender point and referred pain at several different clinics.

He had received conservative treatments such as physical therapies and oral medication. Repeated trigger point in- jection with lidocaine were also received for 3 years.

However, he reported that none of the conservative treat- ments provided any significant pain relief.

On physical examination in our hospital, a mass (about 2×2 cm in size) was palpated at left middle para-thoracic muscle, erector spinae at the T8-T9 level. There was local tenderness directly on this mass and the location of pain corresponded with this mass area. In addition, referred pain radiating to the left posterolateral thoracic area was provoked. However, there was no taut band and no LTR in the left erector spinae muscle. In summary, he showed a localized spontaneous muscle pain and localized tender- ness with referred pain, after minor muscle strain.

Therefore, the mass had been misinterpreted as the trigger point, palpable nodule in the taut band.

Because there was no improvement of symptom for a long time, a thoracic spine magnetic resonance imaging (MRI) was performed to rule out tumorous lesions. A thoracic spine MRI showed an oval shaped mass (1.5×1.2

×2.1 cm in size) in the left erector spinae muscle at T8∼9 level. This mass showed an iso-signal intensity in T1 weighted image and a high-signal intensity in T2 weighted image. Also, contrast-using image revealed an enhanced mass with sharp margin. It was a suspected neurogenic tu- mor (Fig. 1). The patient was referred to a neurosurgeon and underwent tumor removal. Operative findings revealed that the mass was well-defined, soft, ovoid, yellow-colored, glis- tening and myxoid mass measuring 2×1.5×1.3 cm (Fig. 2).

The final pathologic diagnosis was schwannoma with focal

김강희 외 4인: 근막통증후군으로 오인된 신경초종

CLINICAL PAIN 35 Fig. 3. Pathologic findings of the schwannoma. (A) Low power view (×40) with hematoxylin and eosin stain revealed a well-demar- cated mass with a thick fibrous capsule. Alternating hypercellular and hypocellular areas, Antony A and B tissue pattern were shown, which are typical findings of schwannoma. Calcified foci were also identified. (B) In high power view (×400) with hematoxylin and eosin stain, hypercellular areas consisted of spindle cells with neural differentiation. Palisading nuclei, and Verocay bodies were fre- quently seen.

calcification, which was in concordance with the MRI find- ings (Fig. 3). After excision of the schwannoma, the symp- toms were completely resolved. At two months after tumor removal, he presented no definite pain.

DISCUSSION

MPS has been defined clinically as a regional pain syn- drome characterized by muscle pain caused by MTrPs.

Despite its clinical entity, there is a lack of validated diag- nostic criteria set by international bodies or expert consensus. Therefore, clinicians use different criteria for the diagnosis of MPS.

The most commonly used diag- nostic tools of MPS, which manifests with 1 or more MTrP, is usually based on the patient’s subjective symp- toms and the presence of an MTrP characterized by (1) ten- der spots in 1 or more palpable taut band, (2) a referred pain pattern, (3) a LTR, and (4) restricted range of motion.

However, the presence of an MTrP is a con- troversial subject because patient’s symptoms and signs overlap with other conditions and there are no objective laboratory tests for diagnosing MTrPs.

In this case, there was no palpable taut band, LTR, and restricted range of motion although the patient had a tender spot and a referred pain pattern.

Most clinicians have used a trigger point injection or dry

needling as conservative management of MPS for both di- agnosis and treatment, simultaneously.

However, if there are no reductions of muscular pain after conservative man- agement of MPS, clinicians should consider the possibility of technical factors first. Technical factors for causes of failure in pain relief may include an incomplete inacti- vation of all sensitive loci in an MTrPs region and an ex- cessive damage to muscle fibers or blood vessels. After the exclusion of technical factors, diagnostic factors should be considered such as superimposed fibromyalgia syndrome, neurogenic pain and neoplasm.

Schwannoma is a nerve sheath tumor from schwann cells along the course of a nerve.

They are the commonest tumors of peripheral nerves, and can develop anywhere schwann cells are present. As the schwannoma grows, it can compress adjacent structures such as nerve and soft tis- sue and lead to irritation or damage to the nerve itself.

Pain caused by schwannoma might be numbness or tingling. Because the mass can be accompanied by tender- ness or radiating pain, it can be misdiagnosed as MPS.

In the current case, it took 3 years to correctly diagnose

the schwannoma. Pain characteristics were suggestive of

MPS in erector spinae muscle. However physical examina-

tion revealed a lack of diagnostic criteria for MTrPs. Such

vague symptoms and signs lead to the misdiagnosis of

MPS and inappropriate treatments by many health care

VOL. 13, NO. 1, 2014

CLINICAL PAIN 36

providers. However, after the proper diagnosis of schwan- noma, local excision was successful in improving the pa- tient’s pain.

In conclusion, this case demonstrates that the clinician should suspect other etiologies and conduct imaging studies such as MRI or ultrasonography for accurate diagnosis and proper management, either when a suspected MPS does not fulfill the criteria completely or fails to respond to proper treatment for a prolonged period.

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