Introduction Bilateral anterior horn cell hyperintensity on spinal imaging (‘snake eyes’ sign) is seen in pathologies including cervical spondylosis, spinal cord infarction and Hirayama’s disease. Below is the first report of lower limb monomelic amyotrophy (MMA) with thoracic spine snake eyes sign. We present a case report of lower limb MMA with bilateral anterior horn hyperintensity, and literature review of cases with this clinico-radiologic presentation.

Case A 47 year old man presented with an 11 year history of asymmetric, progressive, proximal right lower limb weakness and wasting following traumatic back injury. Eight years into the disease course left leg changes developed. There was no upper limb, bulbar nor respiratory involvement. Examination revealed widespread lower limb wasting, normal tone, marked proximal weakness, brisk reflexes and non-sustained clonus bilaterally. Upper limb and cranial nerve examinations were normal. MRI demonstrated T11–12 bilateral anterior horn cell hyper-intensity. Electromyography demonstrated denervation/re-innervation changes in the right vastus lateralis and to a lesser extent tibialis anterior. Muscle biopsy showed chronic denervation atrophy. Anti-ganglioside GM1 IgM was elevated. Further autoimmune testing, infectious screen, cerebrospinal fluid and neuromuscular disease gene analysis were negative. Steroid and intravenous immunoglobulin therapy were ineffective.

Case series describing lower motor neuron diseases (LMND) including MMA have not previously reported snake eyes sign in association with lower limb disease.1 Two recent publications describing thirty-two cases of LMND with cervical spine snake eyes sign report that all cases were associated with a relatively benign course and many were misdiagnosed as motor neuron disease (MND).2 3 The authors propose this as a previously unidentified mimic of motor neuron disease.

Conclusion This is the first reported case of thoracic snake eyes sign with corresponding lower limb MMA. Lower motor neuron diseases with bilateral anterior horn cell hyper-intensity may represent a unique clinical form of MND with relatively slower progression.