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Electromyogram-evoked focal myositis.

Focal myositis or focal nodular myositis is an entity that presents as localized pain and swelling over a muscle group of an extremity. It was first described during the 1970s but has remained a rare disorder with <100 cases reported. The underlying etiology is a mystery, but eliciting microtrauma has been suggested. We present a case demonstrating that iatrogenic trauma from an electromyogram potentiated a recurrent episode of focal myositis.

CASE DESCRIPTION

A 74-year-old black man with prior chronic obstructive pulmonary disease and hypertension presented with a 3-day history of right calf swelling, dark discoloration, and pain. These symptoms began abruptly and were independent of any inciting trauma, fever, chills, or skin breakdown. The pain was localized within the calf muscle and worsened with dorsiflexion of the foot. He was hemodynamically stable and afebrile. Physical examination was unremarkable with no additional lesions or apparent muscle weakness. The erythrocyte sedimentation rate was 40 mm/hr with a C-reactive protein level of 7 mg/dL. The white blood cell count and creatinine kinase level were within normal limits. Magnetic resonance imaging demonstrated inflammation of the gastrocnemius muscle concerning for myositis (Figure 1a). Antibiotics were initiated but blood cultures returned negative. The right calf swelling, discoloration, and tenderness persisted. Antinuclear antibody was positive at a titer of 1:1280, and a myositis-specific antibody panel was performed. It revealed negative anti-Mi-2, PL-7, PL-12, EJ, OJ, Ku, and U2 snRNP antibodies. In addition, antibodies against 3-hydroxy -3-methylglutaryl-coenzyme A reductase were not present. Muscle biopsy disclosed superficial necrosis but normal muscle tissue and fascia within centimeters of exploration. Extracellular edema was present without overt signs of infection or hematoma formation. Microscopic examination of the muscle tissue revealed viable muscle and small numbers of lymphocytes that stained negative for IgG4 (1). In addition, scattered eosinophils were present but not in significant numbers. Gram stain and acid-fast and fungal stains were negative. There was marked variation in myofiber size (Figure 1d) along with CD163-positive macrophages located within the perimysium (Figure 1c).

Given his positive antinuclear antibody, methylprednisolone was started. Rheumatoid factor, ANCA, anti-Jo, anti-Ro, anti-La, anti-Smith, anti-RNP, anti-Scl70, anti-smooth muscle and anti-striated muscle antibodies were all within normal limits or negative. However, there was a positive result for an anti-centromere antibody.

A potential neoplasm was ruled out with negative esophagogastroduodenoscopy, colonoscopy, serum and urine electrophoresis, and computed tomography scans of the chest, abdomen, and pelvis. An electromyogram revealed slightly increased polyphasic potentials and abnormal spontaneous activity in the left anterior tibialis and gastrocnemius muscles. Otherwise, all remaining muscles showed no evidence of electrical instability or conductive disorders. Following the electromyogram, the patient developed three new focal lesions. These were similar in appearance to the initial lesion on admission but were not as severely swollen. They were located in the left gastrocnemius, left deltoid (Figure 1b), and left abductor pollicis brevis muscles. Each of these muscles had overlying skin discoloration and a pain that worsened by muscle contraction. His erythrocyte sedimentation rate was 100 mm/hr despite the high-dose methylprednisolone. Rituximab infusions were initiated with subsequent resolution of the lesions. Ultimately, he was discharged to a skilled nursing facility and has not had recurrent lesions after 2 years.

DISCUSSION

Focal myositis was first described in 1977 by Reid Heffner Jr. He described 16 cases of myositis within a muscle group of an extremity. The myositis was not preceded by trauma or related to infection, but appeared to be a benign pseudotumor of skeletal muscle. Creatinine phosphokinase and lactate dehydrogenase levels were within normal limits, and the erythrocyte sedimentation rate was normal in 10 of the 16 patients. The muscle demonstrated no significant areas of necrosis, hemorrhage, or calcification. However, a "pale, ovoid and poorly defined area" of muscle was described in 11 of the 16 cases. Histologically, there was striking variation in muscle fiber size, with no predominance of fiber type. Phagocytic activity within the muscle fibers was often intense, and inflammatory infiltrates, particularly lymphocytes, were overshadowed by the myopathic fiber changes. Treatment in Heffner's study was primarily surgical, but 8 cases simply had a muscle biopsy alone. None of the patients developed signs of systemic disease or diffuse muscle involvement. Based on these findings, Heffner speculated that, despite no obvious trauma, a subclinical internal injury was responsible for the condition (2).

Diagnosis of focal myositis in our patient was based upon the clinical manifestation of focal inflammation of a muscle group (3), elevated erythrocyte sedimentation rate, and exclusion of an alternative process. He did not have any proximal or distal muscle weakness to suggest polymyositis, dermatomyositis, or inclusion myositis. Furthermore, the myositis-specific antibody panel ruled out those syndromes. Antibodies against 3-hydroxy-3-methylglutaryl-coenzyme A reductase evaluated for a potential necrotizing myopathy associated with statin exposure (4), but was negative.

A unique aspect of our patient's myositis was the provoked recurrence of the disease. The electromyogram revealed focal muscle irritability, but there was no evidence of a diffuse myopathic disorder. Nonetheless, the micro trauma of the procedure potentially provided a stimulus for a myositic event. Other case reports of focal myositis mentioned the use of an electromyogram (5), but did not report an incidence of induced myositic changes. Thus, it is unclear why a recurrence of myositis was seen in our patient and if his autoimmune process increased the immune sensitivity to a specific muscular antigen. However, this incident at least reopens the discussion concerning Dr. Heffner's suspicion that subclinical trauma played a role in inciting focal myositis.

(1.) Auerbach A, Fanburg-Smith JC, Wang G, Rushing EK. Focal myositis: a clinicopathologic study of115 cases of an intramuscular mass-like reactive process. Am] SurgPathol 2009;33(7):1016--1024.

(2.) Heffner RR Jr, Armbrustmacher VW, Earle KM. Focal myositis. Cancer 1977;40(1):301-306.

(3.) Kisielinski K, Miltner O, Sellhaus B, Kruger S, Goost H, Siebert CH. Recurrent focal myositis of the peroneal muscles. Rheumatology 2002;41 (11) : 1318-1322.

(4.) Allenbach Y, Benveniste O. Acquired necrotizing myopathies. CurrOpin Neurol 2013;26(5):554-560.

(5.) Gordon M, Madhok R. Recurrent focal myositis. Rheumatology (Oxford) 1999; 38 (12): 1295-1296.

Avery Smith, MD, George Snipes, MD, and Carolyn Quan, MD

From the Departments of Internal Medicine (Smith, Quan) and Pathology (Snipes), Baylor University Medical Center at Dallas.

Corresponding author: Avery Smith, MD, Department of Internal Medicine, Baylor University Medical Center at Dallas , 3500 Gaston Avenue, Dallas, TX 75246 (e-mail: Avery.Smith@baylorhealth.edu).
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Author:Smith, Avery; Snipes, George; Quan, Carolyn
Publication:Baylor University Medical Center Proceedings
Article Type:Clinical report
Date:Jan 1, 2017
Words:1056
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