J Neurol DOI 10.1007/s00415-014-7580-8
LETTER TO THE EDITORS
‘Snake eyes’ MRI sign: possible role of cobalt toxicity? Chiara Briani • Mario Cacciavillani • Annamaria Nicolli • Andrea Trevisan Roberto Gasparotti
Received: 4 September 2014 / Revised: 4 November 2014 / Accepted: 6 November 2014 Ó Springer-Verlag Berlin Heidelberg 2014
Dear Sirs, ‘Snake eyes’ sign is the magnetic resonance imaging (MRI) occurrence of bilateral hyperintensities of the anterior horns of spinal cord on axial T2-weighted MR images. This neuroradiological sign has been commonly attributed to lower motor neuron (LMN) syndromes, such as Hirayama disease, but also in cervical spondylotic myelopathy and spinal cord infarction. Recently Lebouteux et al.  dissected the evidence for, and against, the possible association of MRI snake eyes with LMN syndromes thanks to a follow-up study that allowed analysis of the evolution of patients with MRI snake eyes sign and clinical-electrophysiological evidence of upper limb LMN degeneration. In this cohort of patients, none eventually developed amyotrophic lateral sclerosis; in 62.1 % no specific etiology was found, and idiopathic LMN syndrome was diagnosed. We report on a patient with upper limb LMN syndrome and MRI snake eyes sign secondary to cobalt neurotoxicity.
C. Briani (&) Department of Neurosciences, Sciences NPSRR, University of Padova, Via Giustiniani 5, 35128 Padua, Italy e-mail: [email protected]
M. Cacciavillani EMG Unit, Data Medica Group, CEMES, Padua, Italy A. Nicolli A. Trevisan Department of Cardiologic, Thoracic and Vascular Sciences, University of Padova, Padua, Italy R. Gasparotti Department of Medical and Surgical Specialties, Radiological Sciences and Public Health, University of Brescia, Brescia, Italy
A 42-year-old man, technical assistant of a soccer team who currently plays soccer and goes to gym, came to our attention for subacute left upper limb weakness (triceps 3/5 MRC; wrist digits extensor, abductor pollicis brevis, first dorsal interosseous, abductor digiti minimi 4/5 MRC) with no sensory disturbances. The left first dorsal interosseous muscle showed mild atrophy. Right upper limb and lower limbs had preserved strength and sensation. Deep tendon reflexes were present. Neurophysiological evaluation revealed normal sensory and motor conduction studies and bilateral neurogenic changes in triceps, pectoralis, extensor carpi radialis, extensor digitorum communis, flexor carpi radialis and ulnaris, abductor pollicis brevis, first dorsal interosseous, abductor digiti minimi muscles, more severe on the left side, data consistent with upper limb LMN degeneration (C7-C8-T1 levels). No median, ulnar, and radial nerves abnormalities were detected by ultrasound bilaterally. In his medical history, otherwise uneventful, the patient had undergone hip replacement for severe osteoarthritis (attributed to an abnormal position of the hip during sport activities) in May 2007 with a cobalt–chromium prosthesis. When we first saw the patient (December 2012), he had been complaining of symptoms for about 3 months; blood cobalt and chromium were 14.3 and 11.1 lg/L, respectively (normal range: cobalt 0.05–0.1 lg/L, chromium 0.1–0.5 lg/L), exceeding the Medicines and Healthcare Products Regulatory Agency acceptable blood cobalt concentration (below 7 lg/L). Extensive blood tests, comprehensive of infectious, neoplastic, metabolic, endocrine, and immunological markers, all resulted negative ruling out other identifiable causes of LMN syndrome. Cerebrospinal fluid analysis was negative (protein 37 mg%, 1 WC/lL, no oligoclonal bands); cobalt and chromium values were unremarkable.
Fig. 1 MRI of the cervical spine, sagittal (a) and axial (C6–C7) (b) T2W sections. Cervical myelopathy with bilateral symmetric hyperintensities in the anterior horns, extending from C4 to C7 (a), characterized by a ‘‘snake eyes’’ appearance on the axial T2W sections (b)
A LMN syndrome of the upper limbs secondary to cobalt release from the hip prosthesis [3–7] was, therefore, considered. Our patient did not present with hearing loss, visual disturbances, hypothyroidism and/or cardiomyopathy, symptoms commonly described in cobalt toxicity. However, the increased blood cobalt concentration after hip replacement, the fall of blood cobalt and the clinicalneurophysiological improvement after prosthesis removal, strongly support a cobalt-mediated LMN syndrome. Also, the bilateral involvement supports a systemic toxic pathogenesis. The present case, while confirming the association of MRI snake eyes sign with upper limbs LMN syndrome, points to a likely neglected  different cause of snake eyes sign and LMN degeneration, that might be considered in the diagnostic process. Conflicts of interest of interest.
Cervical spine MRI revealed bilateral hyperintensities into the anterior horns of cervical spinal cord, extending cranio-caudally from C4 to C7 with mild cord atrophy (Fig. 1a) and a typical snake eyes pattern in T2-weighted axial sections (Fig. 1b). Brachial plexus MR Neurography was unremarkable. In the following months, patient’s conditions slowly deteriorated and hip prosthesis was removed. In March 2014, 6 months after hip prosthesis removal, blood and urine cobalt and chromium levels dropped close to reference values (Graphite furnace atomic absorption spectrophotometer Perkin-Elmer AAnalyst 600 with Zeeman effect background correction was used to analyze metals in whole blood). Clinically, triceps muscle strength improved (4/5 MRC). Electromyography showed bilateral increased motor unit recruitment at triceps, pectoralis, extensor digitorum communis, flexor carpi radialis and ulnaris, abductor pollicis brevis muscles. On the basis of the relatively older age of the patient and of the absence of detachment of the posterior dural sac from the subjacent laminae on axial T2-weighted MR images obtained in neutral position, Hirayama disease was considered unlikely .
The authors declare that they have no conflict
Ethical standard The patients gave informed consent to the study, which has been performed in accordance with the ethical standards of Helsinki declaration.
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