A Rare Lower-Extremity Presentation of Multifocal Motor Neuropathy (MMN) Prior to Upper-Extremity Involvement

Multifocal motor neuropathy (MMN) is a rare motor neuron condition that typically presents as asymmetric muscular dystrophy to the distal upper extremities. As an autoimmune disorder, it is hypothesized that the presence of anti-ganglioside-monosialic acid 1 (anti-GM1) antibodies results in demyelination of axons, propagating symptoms of MMN. Intravenous immunoglobulin infusions have proven effective in restoring muscle tone and function if administered at early onset of the disease symptoms. Although uncommon, MMN can also affect the distal lower extremities. In this study, we present a female patient with muscle atrophy and general weakness to her right lower extremity prior to developing similar symptoms to her left upper extremity. Due to this very uncommon presentation, the pathology was identified late in the progression of the disease. The delay in treatment resulted in a permanent reduction in muscle tone and function in the right lower extremity. To the best of the authors' knowledge, such a finding has not been reported in the current literature, prompting the need for awareness of a truly uncommon presentation of an already uncommon condition.