Madras motor neuron disease (MMND) is a rare childhood or juvenile motor neuron disease. Herein, we present a unique case of MMND in an 18-year-old patient, which challenges the conventional understanding of the disease's onset and progression. The patient, a previously healthy adolescent, presented with insidious onset and gradually progressive weakness of all four limbs, wasting, tongue fasciculation, and bilateral sensorineural hearing loss. Neurological examination revealed signs consistent with lower motor neuron involvement. Electromyography (EMG) and nerve conduction studies (NCS) supported the diagnosis of MMND. The patient's clinical course exhibited rapid deterioration, leading to significant functional impairment within a short timeframe. Treatment modalities, including supportive care and symptomatic management, were implemented; however, disease progression remained relentless. This case highlights the significance of considering MMND in the differential diagnosis of motor neuron diseases, even in young individuals. It highlights the importance of conducting more studies to comprehend the underlying mechanisms and consider potential therapeutic strategies for this uncommon ailment.

A 34-year-old Chinese Han female complaining of general muscle weakness and wasting for 9 years. She was admitted for aggravation of her symptoms caused by respiratory distress. She also suffered from bulbar palsy. She had no hearing loss, visual problems, or cerebellar signs. Her parents had a consanguineous marriage, though there was no family history of these symptoms. Pure tone audiometric findings demonstrated no definite abnormality. Electromyography demonstrated neurogenic damage. Brain magnetic resonance imaging revealed cerebellar atrophy, dominantly in anterior lobe. Gene sequencing of whole gene exomes was negative. She was finally diagnosed with Madras motor neuron disease (MMND), a rare subtype of motor neuron disease. No definite therapy was available for MMND, and she died of respiratory tract infection 1 year later. Previous studies have shown that cerebellar signs are positive in 17.2% patients of MMND, but no case with cerebellar atrophy has been reported before. Thus, here we describe cerebellar atrophy as a new clinical feature of MMND.