Application of High-resolution Ultrasonography for the Diagnosis of a Case With Sports-related Sural Neuritis

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1 C A S E R E P O R T Application of High-resolution Ultrasonography for the Diagnosis of a Case With Sports-related Sural Neuritis Tsung-Ching Lin 1, Hsiu-Ling Chou 2, Hong-Jen Chiou 3, Cheng-Ming Chiu 1 *, Cheng-Liang Chou 4, Rai-Chi Chan 4 Entrapment and compression of peripheral nerves of the lower extremities, such as the sural nerve, are known to be infrequent sequelae of injuries resulting from exercise, posture, or footwear. Although testing for Tinel s sign and nerve conduction velocity examinations contribute to an accurate diagnosis, the use of high-resolution ultrasonography is preferred, not only because of its cost-effectiveness and non-invasive dynamic capacity, but also because of difficulty in differential diagnosis due to the overlapping sensory distribution of peripheral nerves. This report describes the use of high-resolution ultrasonography and nerve conduction examination of the sural nerve in a case of sural neuritis attributed to a sports-related ankle sprain. KEY WORDS sprain, sural neuritis, ultrasonography J Med Ultrasound 2009;17(3): Introduction The sural nerve is a sensory nerve that branches from the tibial nerve in the popliteal fossa and descends between the heads of the gastrocnemius muscle, traversing laterally to the Achilles tendon and inferiorly to the peroneal tendon sheath [1]. At the base of the fifth metatarsal bone, it bifurcates into its lateral and medial terminal branches, providing sensory innervation to the lateral aspects of the ankle, heel, and foot [2]. Entrapment and compression of peripheral nerves due to fibrotic scar encasement, soft tissue or tendon edema, or direct nerve damage are infrequent sequelae of injuries resulting from repetitive, prolonged, or intense exercise [3]. In athletes, sural neuropathies have been reported to occur as a result of entrapment where the nerve exits the fascia in a fibrotic aponeurosis, and further exacerbation over time by prolonged compression over the entrapment site [4] and plantar flexion [5]. Complete recovery is expected after decompression in most cases, although chronic high pressure at the site of entrapment may significantly alter nerve morphology Received: December 10, 2008 Accepted: February 23, The Division of Physical Medicine and Rehabilitation, Far Eastern Memorial Hospital, 2 Department of Nursing, 3 Department of Radiology, and 4 Department of Physical Medicine and Rehabilitation, Taipei Veterans General Hospital, Taipei, Taiwan. *Address correspondence to: Cheng-Ming Chiu, Division of Physical Medicine and Rehabilitation, Far Eastern Memorial Hospital, 21, Nan-Ya South Road, Section 2, Pan-Chiao, Taipei, Taiwan. E mail: tommychiu777@yahoo.com.tw 178 J Med Ultrasound 2009 Vol 17 No 3 Elsevier & CTSUM. All rights reserved.

2 High-resolution Ultrasonography in Sural Neuritis and conduction function, often with subsequent sensory or motor impairments, depending on the types of nerves affected. Current recommendations for diagnosis of peripheral nerve injuries by the American Association of Neuromuscular and Electrodiagnostic Medicine are testing for Tinel s sign and nerve conduction velocity examination, including both motor and sensory tests of the impinged nerves [6]. However, with regard to the sural nerve, these tests are not always specific because of the lateral sensory distribution of the nerve, with symptoms often misdiagnosed as Achilles tendinopathy [7]. High-resolution ultrasonography (HRUS) is increasingly being used in the diagnosis of peripheral nerve disorders. It is considered an optimal imaging technique in this field because it can provide non-invasive, low-cost, dynamic, rapid, and detailed imaging of all major peripheral nerves in both the upper and lower extremities [8 10]. To our knowledge, no previous reports have been published on the use of HRUS for diagnosis of sural neuritis. We present the case of a 30-year-old professional dancer who was diagnosed with sural neuritis on the basis of HRUS and nerve conduction examination. Case Report A 30-year-old female professional dancer complained of persistent painful swelling and paresthesia on the dorsolateral aspect of her right ankle for duration of 8 weeks. There was no significant medical history. The patient was admitted to our rehabilitation outpatient clinic. She attributed the symptoms to an ankle sprain that she had sustained 8 weeks earlier during dance practice. The injury was followed by progressive pain and swelling. Before presenting at our clinic, she had undergone treatment with acupuncture and adhesive patches formulated with traditional Chinese medicine. These treatments were not effective. At another local clinic she was diagnosed with suspected tendonitis. On the day of admission to our clinic, physical examination revealed reduced sensitivity to temperature and Fig. 1. Local swelling over the right lateral malleolus area on physical examination (cross indicates the sural nerve). Sural N Fig. 2. Longitudinal scan shows a focal hypoechoic change with swelling of the right sural nerve (arrow) over the ankle region distal to the gastrocnemius muscle in the period of initial diagnosis. The nerve is 0.21 cm in width. (GE Logiq 700MR, Milwaukee, WI, USA with M12L linear probe) palpation on the dorsolateral aspect of her right foot. Tenderness over the right gastrocnemius muscle with mild swelling was found. Significant local swelling over the right lateral malleolus area and a decreased range of motion were also observed (Fig. 1). An HRUS examination (GE Logiq 700MR, Milwaukee, WI, USA; M12L with an M12L linear probe) showed a focal hypoechoic change and swelling of the right sural nerve distal to the gastrocnemius muscle. The width of the right sural nerve was 0.21 cm (Fig. 2). Electrodiagnosis was used to measure nerve conduction velocity. The examination included measuring motor conduction of the peroneal and tibial nerves, and sensory E3 J Med Ultrasound 2009 Vol 17 No 3 179

3 T.C. Lin, H.L. Chou, H.J. Chiou, et al Table 1. Nerve conduction examination results Latency (msec) Conduction velocity (msec) Amplitude (mv) Distance (cm) Distal peroneal nerve Left Right Proximal peroneal nerve Left Right Distal tibial nerve Left Right Proximal tibial nerve Left Right Sural nerve Left Right conduction of the sural nerve. The peroneal nerve was stimulated below the fibula head and on the dorsum of the ankle. A recording electrode was placed on the extensor digitorum brevis muscle. The tibial nerve was stimulated in the popliteal fossa and above the medial malleolus; a recording electrode was placed on abductor hallucis muscle. The sural nerve was antidromically stimulated at the lateral midline of the posterior aspect of the calf. Recordings were obtained from an electrode placed over the sural nerve where it is posterior and inferior to the lateral malleolus [11,12]. At the time of the electrodiagnostic examination the mean skin temperature of the patient was 31 C. The results indicated that the distal latency of the right sural nerve was mildly prolonged and the conduction velocity was decreased in comparison with the left sural nerve (Table 1). The patient was prescribed physical therapy twice a week which consisted of transcutaneous electrical nerve stimulation with therapeutic ultrasound applied over the swelling site. In addition, the patient was prescribed 5 mg of oral prednisolone twice a day for 7 days. After 1 month of physical therapy she had a reduction in pain and swelling at the affected site. At 1-month follow-up an HRUS examination (Philips HDI 5000 SonoCT, Bothwell, WA, USA with a 5 12 MHz linear array) was performed. There was improvement in the focal hypoechoic change and a reduction in the width of the right sural nerve to 0.16 cm (Fig. 3). At 6-month follow-up the patient demonstrated complete recovery. Discussion Although peroneal and sural neuropathies are rare, they have been reported in dancers [13]. In the present case, we observed mild swelling of the right gastrocnemius muscle of a female professional dancer. It is possible that impaired venous flow attributed to direct nerve injury and compression from the injured gastrocnemius muscle resulted in reversible intraneural edema, which probably contributed to the partial enlargement of the sural nerve. We believe that had the patient not received prompt and effective treatment, isolated sural neuropathy would have remained subclinical, and neurologic injury would have eventually resulted from prolonged compression, requiring surgical intervention [4]. Chronic impingement of peripheral nerves 180 J Med Ultrasound 2009 Vol 17 No 3

4 High-resolution Ultrasonography in Sural Neuritis A B Sural N 1 Sural N Fig. 3. Longitudinal scan shows (A) Improvement in the focal hypoechoic change and swelling of the right sural nerve (arrowhead); right sural nerve thickness decreased to 0.16 cm after 1 month of rehabilitation management, and (B) Left sural nerve (arrowhead) over ankle region. (Philips HDI 5000 SonoCT, Bothell, WA, USA with 5 12 MHz linear array) is known to contribute to ischemia and irreversible internal fibrosis as a result of damage to the vasa nervorum, the small vessels responsible for vascularization of the nerve trunk. Diagnosis of sural neuropathy is difficult because most peripheral nerve disorders are symptomatic only during functional activity and involve overlapping sensory distribution [3]. In our case, motor nerve conduction velocity examination, although less sensitive than sensory nerve conduction examination, revealed prolonged sural nerve latency and decreased nerve conduction velocity, indicating impingement somewhere between the gastrocnemius heads. These findings were confirmed by HRUS, which also revealed the morphologically altered sural nerve in relation to the heterogeneous hypoechoic areas of the gastrocnemius muscle. High-resolution ultrasonography can be a supplement to the conventional radiography in the evaluation of musculoskeletal soft-tissue masses in children [14]. Musculoskeletal ultrasonography can also detect tissue damage, such as the greatest meniscal subluxation in knees, early before the appearance of radiographic signs of osteoarthritis [15]. High-resolution ultrasonography offers significant advantages over magnetic resonance imaging in the imaging of peripheral nerves, including higher spatial resolution, real-time imaging of joint movements, better contrast resolution, and increased differentiation of nerve anatomy in relation to surrounding structures [8 10]. It is also more economical, requiring less advanced technology, and it obviates absolute immobilization of the patient, which is difficult to achieve. Development of quantitative ultrasound techniques in the evaluation of tissue quality and organization of tendinopathy may be helpful in the differential diagnosis of sural neuritis secondary to multiple neuropathies, as in most cases with sural nerve involvement [16]. In summary, HRUS is an objective method to confirm the clinical diagnosis after physical examination. Furthermore, it is possible to gain not only qualitative but also quantitative data. Treatment of sural neuritis, which is similar to that of mild peripheral nerve disorders of the lower extremities, is conservative and includes physiotherapy, corticosteroids, nonsteroidal anti-inflammatory drugs, and footwear modifications. Eliminating excessive pronation and any mechanics that inhibit healing is important, especially in professional dancers. Complete resolution of symptoms has been reported 4 months after cessation of dancing [17]. In cases of delayed diagnosis and prolonged compression and fibrotic scar encasement of the sural nerve, surgical intervention is indicated [4]. In conclusion, the diagnosis of sural neuropathy is based on clinical presentation and electrodiagnostic examination. HRUS is only an adjunct to the accurate diagnosis. A combination of sensory nerve conduction examination and HRUS is useful J Med Ultrasound 2009 Vol 17 No 3 181

5 T.C. Lin, H.L. Chou, H.J. Chiou, et al for diagnosing sural neuropathies attributed to sports-related injuries. Disorders of the sural nerve due to sprains and strains may be underdiagnosed, especially in patients involved in professional sports activities such as dancing. Further studies evaluating sport-specific injuries to the peripheral nervous system are recommended. References 1. Mestdagh H, Drisenko A, Maynou C, et al. Origin and make up of the human sural nerve. Surg Radiol Anat 2001;23: Sarrafian SK. Anatomy of the Foot and Ankle: Descriptive Topographic Function, 2 nd edition. Philadelphia: JB Lippincott, Rosenow DE. Superficial peroneal nerve. J Neurosurg 2007;106: Bryan BM III, Lutz GE, O Brien SJ. Sural nerve entrapment after injury to the gastrocnemius: a case report. Arch Phys Med Rehabil 1999;80: Fabre T, Montero C, Gaujard E, et al. Chronic calf pain in athletes due to sural nerve entrapment: a report of 18 cases. Am J Sports Med 2000;28: American Association of Neuromuscular and Electrodiagnostic Medicine. Usefulness of electrodiagnostic techniques in the evaluation of suspected tarsal tunnel syndrome: an evidence-based review. Muscle Nerve 2005;32: McCrory P, Bell S, Bradshaw C. Nerve entrapments of the lower leg, ankle and foot in sport. Sports Med 2002;32: Bianchi S, Martinoli C, editors. Ultrasound of the Musculoskeletal System. Berlin: Springer-Verlag, Peer S, Bodner G, eds. High-Resolution Sonography of the Peripheral Nervous System, 2 nd edition. Berlin: Springer- Verlag, Stuart RM, Koh ES, Breidahl WH. Sonography of peripheral nerve pathology. AJR Am J Roentgenol 2004; 182:123e Preston DC, Shapiro BE. Electromyography and Neuromuscular Disorders: Clinical-Electrophysiologic Correlations. Butterworth-Heinemann, 1998: Schuchmann JA. Sural nerve conduction: a standardized technique. Arch Phys Med Rehabil 1977;58: Sammarco GJ, Miller EH. Forefoot conditions in dancers: part II. Foot Ankle 1982;3: AbiEzzi SS, Miller LS. The use of ultrasound for the diagnosis of soft-tissue masses in children. J Pediatr Orthop 1995;15: Ko CH, Chan KK, Peng HL. Sonographic imaging of meniscal subluxation in patients with radiographic knee osteoarthritis. J Formos Med Assoc 2007;106: Kibler WB, Goldberg C, Chandler TJ. Functional biomechanical deficits in running athletes with plantar fasciitis. Am J Sports Med 1991;19: Kukowski B. Suprascapular nerve lesion as an occupational neuropathy in a semiprofessional dancer. Arch Phys Med Rehabil 1993;74: J Med Ultrasound 2009 Vol 17 No 3