Case Presentation: A previously healthy 13-year-old male presented with a chief complaint of lower back pain and rash for the past 3 weeks. Associated symptoms included profuse sweating and 10/10 lower back pain radiating to his legs that had progressed in severity with inability to ambulate. On additional questioning, other symptoms included nausea, vomiting, diffuse abdominal pain, and an associated weight loss of 18kg. He also complained of some neck stiffness, and hallucinations. On exam, the patient had persistently high blood pressure (150s/90s). He had red, raised lesions on his upper and lower extremities particularly on the dorsal aspect of his soles as well as on his waist, axillary areas, chest, upper back, abdomen, and genitalia. The patient also had irregular and visible muscle contractions along his posterior lower extremities consistent with myokymia. Sensory, gait, and cerebellar examinations were unremarkable and reflexes were symmetric (2/4).
He was treated empirically with antibiotics at presentation along with labetalol for hypertension and acetaminophen, ketorolac and morphine for pain control. Wound care and dermatology were involved because of the severity of his skin degradation that ultimately resulted in initiation of topical steroids and gabapentin to cease the itching. He was treated with several antihypertensives, and ultimately treated with amlodipine and clonidine. After his initial work up including imaging, laboratory assessment for urinary catecholamines and other possible etiologies for his autonomic symptoms, the diagnosis of Morvan Syndrome was considered. Confirmatory testing for voltage-gated potassium channel antibodies was obtained and EMG/nerve conduction studies were consistent with fibrillary chorea. He was initially treated with steroids and then treated with IVIG for five days (1 mg/kg/day). He had slow improvement and was able to be discharged with medications for pain control, muscle spasm and two anti-hypertensives. He showed slow but steady improvement with incremental resolution of his symptoms. After discharge, voltage gated potassium channel antibody testing returned positive.
Discussion: Morvan syndrome is a series of symptoms characterized primarily by peripheral nerve hyperexcitability causing painful cramps, myokymia and neuromyotonia as well as other symptoms such as hallucinations, myoclonus, and hyperhidrosis. Although the syndrome was described in 1890, it remains a rare diagnosis with only 27 documented cases in English literature. The primary pathophysiology remains consistent across all reviewed cases in literature as an autoimmune antibody response to voltage-gated potassium channels.
Conclusions: Although the epidemiology and trigger behind why our patient developed Morvan syndrome is still unknown, it is important to recognize the occurrence of Morvan syndrome especially at a pediatric level and initiate prompt treatment. It is also important to note that due to the resulting time delay for specific VGKC antibody testing, EMG/Nerve Conduction Study waveforms that correspond with Morvan syndrome can play an important role in successful treatment for the pediatric patient. Ultimately, the clinician should be aware of the clinical triad of myokymia, hyperhidrosis, and hallucinations as consistent with Morvan syndrome and maintain an index of suspicion for this rare disorder.