Intercostal nerve mononeuropathy: study of 14 cases

Arq Neuropsiquiatr 2005;63(3-B):776-778 INTERCOSTAL NERVE MONONEUROPATHY Study of 14 cases Paulo Sergio S. dos Santos1, Luiz Antonio Lima Resende2, Ronaldo G. Fonseca2, L. Lemônica1, Raul Lopes Ruiz Jr3, Antonio José M. Catâneo3 ABSTRACT - This re t rospective study describes 14 cases of intercostal nerve mononeuropathy (INM) found in 5,560 electromyography (EMG) exams perf o rmed between January 1991 and June 2004 in our University Hospital. Medical charts of all patients with history of thoracic pain and EMG diagnosis of intercostal mononeuropathy were reviewed. INM was detected in 14 patients; etiology was thoracic surg e ry in 6 (43%), post-herpetic neuropathy in 4 (28%), probable intercostal neuritis in 2 (14%), lung neoplasia in 1 (7%), and radiculopathy in 1 (7%). From this study, trauma and infection were the main etiologies in intercostal neuropathic pain development. Tricyclic antidepressants and anticonvulsants were the most common therapeutic drugs used. KEY WORDS: intercostal mononeuropathy, EMG, etiology. Mononeuropatia de nervo intercostal: estudo de 14 casos RESUMO - Este trabalho apresenta estudo re t rospectivo de 14 pacientes com mononeuropatia de nerv o intercostal (MNI), obtidos dentre 5.560 exames eletromiográficos, realizados de janeiro de 1991 até junho de 2004, em nosso Hospital Universitário. MNI foi encontrada em 14 pacientes, tendo como causas prováveis intervenções cirúrgicas torácicas em 6 (43%), neuropatia por herpes-zoster em 4 (28%), pro v á v e l neurite de nervo intercostal em 2 (14%), neoplasia pulmonar em 1 (7%) e radiculopatia em 1 (7%). As principais causas de MNI de nosso Serviço são similares às da literatura. Os antidepressivos tricíclicos e anticonvulsivantes foram os fármacos mais utilizados no controle da dor. PALAVRAS-CHAVE: mononeuropatia intercostal, EMG, etiologia. The first descriptions of intercostal nerve mononeuropathy (INM) were re p o rted by USA army surgeons treating patients with chronic pain after t h oracotomy as a result of thoracic trauma during the Second World War1. There is an estimated 11 to 80% incidence of chronic pain after thoracotomy2, but c h ronic pain tends to reduce over time3. High doses of analgesics consumed during the first week after s u rg e rymay be a risk factor for pain after thoracotomy3. However, low-dose treatment of post-surgical pain induces the liberation of stress related chemical mediators, which may cause pulmonary, cardiovascular, metabolic and neuroendochrine disturbances4. Despite these clinical problems, int e rcostal nerves have been transferred to the bra- chial plexus to treat traumatic brachial plexopathy with minimal effects on pulmonary function5. The first clinical descriptions related to Varicella zoster were in the XIX century6. Infection by Va r icella zoster is also a common cause of INM7, usually presented as unilateral vesicular eruption in a beltlike distribution mainly on the thoracic sensory d e rmatomes, most cases preceded by pain and pare sthesias. The prognosis is usually good, most cases p resents complete re c o v e ryor significant impro v ement7. Atypical clinical presentations are described in imunosupressed patients7. The objective of our study is to describe INM found in our Service, diagnosed by electromyography (EMG). Services of Anesthesiology1, Neurology2, and Thoracic Surgery3, Botucatu School of Medicine, Unesp, Botucatu SP, Brazil Received 22 December 2004, received in final form 16 March 2005. Accepted 6 May 2005. Dr. Luiz Antonio Lima Resende - Department of Neurology and Psychiatry / Botucatu School of Medicine - 18618 Botucatu SP Brazil. E-mail: [email protected] Arq Neuropsiquiatr 2005;63(3-B) 777 METHOD A re t rospective study was made of all patients diagnosed with INM by EMG between January 1991 and June 2004. Patients with insufficient clinical history and physical examination data were excluded. EMG examinations were performed a) in the paravertebral muscles corresponding to the dermatome or myotome where clinical alterations had been re p o rted or found by examination. Concentric needle electodes were i n s e rted 1cm lateral to the corresponding vertebra’s posterior spinous process; or b) in the intercostal muscles, distal to the surgical scar or other visible skin lesion. Electrode insertion was slow, the examiner listening to respirat o ry muscle contraction sounds, and electrode pro g re ssion was stopped when the first clear motor units were seen and heard on re c ruitment to avoid the pneumothorax. Analysis time was set to 10 ms/cm, filter band-pass to 10 - 10,000 Hz, sensitivity to 20 µV/cm (at rest), 200 µV/cm (slight effort) and 1 mV/cm (maximum effort). The exams were obtained using a 2-channel Nihon-Kohden Neuropack 2. The EMG criteria for neurogenic process into the intercostal muscles were a) at rest: presence of fibrillations, positive sharp waves, and/or fasiculations; b) slight eff o rt: elongated duration of motor unit potential; and c) maximum eff o rt: increased amplitude of the motor unit potentials (above 5 mV) and different degrees of rarefaction of the interferential pattern. RESULTS There were 14 cases of INM diagnosed from 5,560 EMG exams (0.25%). Probable etiological diagnoses were a) thoracotomy (6 patients), post-herpetic infection (4), intercostals nerve neuritis (2), lung neoplasia (1), and radiculopathy (1). For the patient with lung neoplasia, impairment of bone, muscles, and intercostal nerve was by contiguity. In some patients with INM after thoracotomy, intercostal nerve imp a i rment was at more than one level, resulting in multiple mononeuropathy (Fig 1). Two patients were diabetic, but no etiological relationship between their INM and diabetes could be found. The most common drugs employed for pain t reatment were tricyclic antidepressants (amitriptilin) and anti-epileptics (carbamazepine). Other d rugs were used; they included non-steroid antiinflamatories, dipirone, and tramadol. In one case, patient controlled analgesy was necessary; fentanil was employed. DISCUSSION I m p a i rment of the intercostal nerves may occur in common clinical conditions such as diabetes8, less frequent pathologies such as neoplasies originat- Fig 1. Lateral aspect of left thorax surgical scar in a patient with mononeuropathy of the left Vth and VIth intercostal nerv e s after thoracotomy ing in the intercostal nerv e s9, or in rare affections, such as sarcoidosis10. Diabetic thoracoabdominal neuropathy usually presents in the 5th and 6th decade, manifests primarily as pain along single or multiple intercostal nerves and may mimic diff e rent conditions as coronary artery disease or apendicitis11. Recently it was published the second brazilian case of INM by benign schwannoma, in a patient with expansive nodular lesion of the 7th coster arch projecting within the left hemitórax12. The more common INM etiologies found in our patients were thoracotomy (43%) and herpes zoster (28%); this is in agreement with literat u re2,3,7,13,14. D i rect injury of the intercostal nerve during thoracic surg e ry is not needed for symptoms to appear, the use of ratcheted rib spreaders may induce INM some distance from the surgical site13. The main clinical problem related to INM is chronic pain that may become debilitating requiring multidisciplinary attention15. Recent published papers highlight the efficacy of anaesthetic block of intercostal nerves in acute16,17 or chronic18 pain profilaxy. In our p atients pain control was possible using common drugs (amitriptine and carbamazepine). In only 1 case was patient controlled analgesy necessary. As far as we know, this is the first description of INM in our country which has been confirmed by EMG. This serious clinical problem which frequently incapacitates has been overlooked in Brazil. More attention needs to be given to this problem. A multidisciplinaryapproach involving neuro l o g i s t s , pain specialists, and thoracic surgeons, could improve quality of life for our INM patients. 778 Arq Neuropsiquiatr 2005;63(3-B) REFERENCES 1. Blades B, Dugan DJ. War wounds of the chest observed at the Thoracic S u rgery Center, Walter Reed General Hospital. J Thorac Surg 1944; 13:294-306. 2. Rogers ML, Duffy JP. Surgical alspects of chronic post-thorac otomy pain. 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