To consider Leprosy in the differential diagnosis of an older patient who presents with demyelinating polyneuropathy.

70-year-old Bangladeshi Man with Diabetes Mellitus presents with two years of distal right arm numbness, right hand weakness, intermittent bilateral feet numbness, and prior blisters on the dorsolateral fingers. Neurologic exam revealed right arm distal>proximal weakness, absent vibration in toes, decreased sensation to pinprick below the right elbow and bilateral ankles, and loss of proprioception of bilateral hallux. During initial skin evaluation no lesions were noted.

Serology was unremarkable including ESR/CRP. EMG/NCS consistent with moderate sensorimotor demyelinating polyneuropathy and possible superimposed right lower trunk brachial plexopathy. MRI C-spine and brachial plexus were unrevealing. Due to EMG results and persistent symptoms Lewis Sumner Syndrome was considered. Ganglioside panel, celiac panel, and CSF studies were normal.

On 3-year follow up, the patient developed worsening weakness and blisters of the left hand, and atrophy of the right hand. Dermatologic exam showed left hand hyperkeratotic plaques, right arm subcutaneous nodules, and hypopigmented patches on the trunk. Biopsy of a hypopigmented patch was negative for AFB. Repeat EMG/NCS showed decreased CMAP and SNAP amplitudes compared to the prior study in bilateral arms with continued ongoing denervation. Left medial antebrachial nerve biopsy confirmed Mycobacterium leprae.

Leprosy is an infectious disease involving the skin, peripheral nerves, mucosal surface of the respiratory tract and eyes. Early diagnosis and treatment are essential to reduce the likelihood of disability as it is often irreversible and requires lifelong care. 

When leprosy occurs exclusively in neuropathic syndromes and at an older age, diagnosis can be difficult. Current classification systems rely heavily on skin manifestations, and diagnosis at the time of only peripheral nerve involvement can become challenging. As information accumulates on various neurological disorders in leprosy, it becomes increasingly clear that treatment paradigms should evolve.