EM or atopic myelitis is defined as a localized myelitis in patients with hyperIgEaemia and mite antigen specific IgE. In spite of the neuropathological features being well described, the exact pathogenesis and clinical features of this disease are not fully understood. Parasitic infection, fungal infection, sarcoidosis, and Churg-Strauss syndrome are thought to be associated with EM. Particularly in Korea, EM patients reported to be positive to Toxocara excretory-secretary (TES) antibody in 93.9%7)
. This is comparable to the fact that seroprevalence of toxocariasis in rural Korean adults was approximately 5%. Also, specific IgE to D. farinae was reported to be detected in 100% of the Korean patients7)
. Characteristic eosinophil infiltration has rarely been encountered in other kind of myelitis and may be a proof of the relation between EM and allergic mechanism.
EM is usually diagnosed by clinical and serologic features, and its pathological confirmation through biopsy is not always compulsory, as in this case study. Several clinical features are known in studies with Japanese patients. 1) stepwise progression and fluctuation of the clinical course, 2) sensory dysfunction as the main symptoms and relatively infrequent motor weakness, 3) myelitic lesion on MRI, 4) Increased IgG in serum and mite antigen-specific IgG positivity, and 5) mild eosinophilia1,5,9,11)
. It is important to make a differential diagnosis of various neurological disorders of the intramedullary lesions. In transverse myelitis, it is usually hard to find the pathogenic factors, and differentiation from intramedullary cord tumor is the main concern to neurosurgeons. When diagnostic confirmation is difficult, physicians usually perform CSF study, various laboratorial tests, or delayed MRI. If intramedullary cord tumor is still suspected, invasive and destructive tissue biopsy may be considered. EM might be considered if stepwise progression or fluctuation of primarily sensory symptom is observed, and sufficient evaluation for allergy should be performed before invasive procedures. The aim of this report is to inform neurosurgeons on the diagnostic tools and clinical characteristics of EM and to avoid the risk of further neurological deterioration by unnecessary invasive spinal cord biopsy.
Various MRI findings are known, and HSI lesion in T2WI, and cord swelling with patchy enhancement are frequently found5,7,9)
. Enhancement of the lesion on post-contrast MRI results from focal blood-spinal barrier disruption due to reactive inflammatory process. Inflammation and infiltrated eosinophils may contribute to the anatomical and functional neural damage8,10)
. Unlike the previous reports, the enhancement was confined to the posterior column in our cases. This finding may explain the restriction of the symptoms to sensory function.
Accumulation of patients' data with EM and their MRI findings should be performed to characterize the enhancing pattern exactly.
EM is clearly related to the allergic mechanism such as elevated serum IgE level and mite antigen-specific IgE positivity. Myelitis with toxocariasis has rarely been reported, even though toxocariasis is a worldwide-occurring parasitic infection. The characteristics of Toxocara myelitis are very similar to those of EM; mainly sensory symptoms, HSI lesion on T2WI MRI, increased IgE and eosinophilia and eosinophilic infiltration on tissue study2,4-6)
. Toxocariasis is caused by Toxocara canis or Toxocara cati in man via incidental consumption of larvae in raw meat or animal liver. The freely migrating larvae can induce immune-mediated hypersensitivity reactions like hyperIgEaemia6,7,11)
. If the larvae migrate to central nervous system, they can cause local inflammation with hypersensitivity reaction and neurological deteriorations3)
. As describe by Lee et al.7)
, many Korean males have a chance of eating raw animal tissue in their social activities. Although exact pathomechanism of the larvae in EM is not well understood, Toxocara myelitis might play a considerable role in provoking EM. A diagnosis of toxocariasis is made by detection of antibody (IgG) for TES-antigen using ELISA method, and this test has high reliability because serologic cross-reaction of toxocariasis is very low2,3,6,11)
. Therefore, we suggest that in case of uncertain myelitis or intramedullary tumorous condition, evaluation for toxocariasis should be done and this might be beneficial. This is the first report illustrating neuropathological findings of EM with proven toxocariasis.
EM has been known to have relatively fair prognosis, because the patient usually present with clinical symptom of stepwise progression without muscle weakness. Systemic steroid administration is known to be effective in controlling clinical symptoms and improving radiologic findings in some cases. In case of toxocara induced EM, antihelminthic drugs like albendazole were reported to be more efficient than conventional steroid therapy in improving clinical status7,11)
. The dose and duration of the administration is not determined.