A case of SPG11-associated hereditary spastic paraparesis identified by the “ear of the lynx sign”

Hereditary spastic paraparesis (HSP) is a genetically and clinically heterogeneous group of disorders with the common feature of progressively worsening spasticity of the lower extremities, often with variable degrees of weakness. Spastic paraplegia type 11 (SPG11) mutations are the most frequent form of autosomal recessive hereditary spastic paraplegia (ARHSP) which represents the complicated form of HSP. Additional features may include cognitive dysfunction, extrapyramidal dysfunction, cerebellar dysfunction or peripheral neuropathy among other features. Imaging findings include a thin corpus callosum although this is not unique to SPG11-related HSP. A characteristic abnormality in these patients affecting the region of the forceps minor of the corpus callosum has been described as the “ears of the lynx” sign. We present a case of a man in his 20s who presented with gradually progressive lower limb spasticity along with weakness, with a history of non-progressive childhood onset action tremors of the right hand. Magnetic resonance imaging (MRI) findings revealed a thin corpus callosum with “ears of the lynx” sign thereby raising the possibility of ARHSP. Electrodiagnostic studies revealed electromyography evidence of both lower motor neuron (LMN) and upper motor neuron (UMN) changes in bulbar and multiple spinal segments with modest fasciculations, scanty fibrillations, and severe spastic recruitment. Whole exome sequencing revealed a compound heterozygous variant in the SPG11 gene thereby confirming the diagnosis of SPG11-related HSP. This case outlines the importance of “ears of the lynx” sign in diagnosis of SPG11-related HSP and simultaneous presence of additional LMN features in SPG11-related HSP, thereby creating a diagnostic overlap with familial amyotrophic lateral sclerosis.