A 76-year-old man with a 5-year history of gait difficulties was suspected to have length-dependent sensorimotor polyneuropathy. Electrodiagnostic results pointed to a foot drop of neurogenic etiology, except for the prominence of myotonic discharges on needle EMG. Tests for acquired and genetic causes of polyneuropathy were unrevealing. The patient's first-degree cousin, with a much different clinical phenotype had been diagnosed with myofibrillar myopathy. Our patient was eventually found to carry the same myotilin c.179C>T p.Ser60Phe mutation. Muscle MRI was helpful in delineating clinically unsuspected involvement of paraspinal and pelvi-femoral muscles, as well as showing marked myopathic fatty infiltration of distal leg muscles. The association of neuropathy and myopathy is a recognized feature of myofibrillar myopathy. In some patients with unexplained foot drop, whole-body muscle MRI and a dedicated genetic mutation testing strategy may help reveal a diagnosis of genetic myopathy.