Case Presentation: A 17-year-old male presented with complaints of worsening muscle spasms and tremors for the past 3 weeks. History was notable for a diagnosis of mercury poisoning about 3 months ago when he presented with back pain, for which he completed a course of succimer. However, he continued to feel unwell despite chelation therapy, developing persistent painful muscle spasms in his legs as well as various neuropsychiatric symptoms, including tremors, insomnia, anxiety, and hallucinations.On exam, he was noted to be anxious and easily distracted. He was tachycardic (120s), hypertensive (140s/80s), and had visible twitching of the muscles in his bilateral thighs. An erythematous macular rash was present on his chest, forearms, and lower legs, and he had desquamation of his hands and feet. He was tremulous in all extremities, but neurological exam was otherwise normal.Initial labs collected were unremarkable except for a urinalysis with proteinuria, confirmed to have non-nephrotic range proteinuria with a urine-to-protein creatinine ratio of 0.54. Nephrology was consulted and recommended a renal biopsy as there was concern for an underlying autoimmune or inflammatory process. Biopsy results showed segmental glomerular capillary IgG deposits suspicious of early membranous glomerulopathy, thought to be due to chronic mercury toxicity.Given his neurological symptoms, Neurology was consulted and he underwent MRI, which was unremarkable. An EMG was performed, which showed frequent spontaneous myokymic discharges. He received methylprednisolone 1 gm for 3 days and rituximab 800 mg once thereafter. He was also started on methocarbamol and gabapentin for symptomatic management of frequent muscle spasms. Psychiatry was consulted for his significant anxiety and insomnia, which were present throughout his hospital stay, and he was started on fluoxetine for his mood and quetiapine to help with sleep.As he reported a history of recent mercury exposure, 24-hour urine collection was done for mercury levels and came back significantly elevated at a level of 530 mcg/L (normal < 20, toxic > 150). Testing for autoimmune encephalitis was sent and ultimately came back positive for CASPR2 antibodies, as well as for voltage-gated potassium channel (VGKC) antibodies with a titer of 229 pmol/L (normal <80), which along with his clinical picture, was consistent with a diagnosis of Morvan syndrome.
Discussion: Morvan syndrome is a rare condition characterized by hyperactivity of the central, peripheral, and autonomic nervous systems secondary to an autoimmune phenomenon. Patients develop insomnia, anxiety, and hallucinations as a result of CNS involvement and characteristically have severe painful muscle spasms, known as myokymia, as a result of peripheral nerve involvement. Tachycardia, hypertension, and hyperhidrosis can occur due to autonomic instability. Although it is a clinical diagnosis, many patients are found to have autoantibodies targeted at the voltage-gated potassium channel, notably at the CASPR2 protein, a component of the complex that makes up the channel. The condition has been associated with heavy metal poisoning, such as gold or mercury, but can also be seen without any obvious trigger, with further testing sometimes revealing an underlying undiagnosed tumor.
Conclusions: In patients with known heavy metal poisoning and ongoing neurological symptoms several months following initial exposure, particularly muscle spasms and neuropsychiatric symptoms, Morvan syndrome must be considered.