The infrequent but curious bacterial myelitis caused, or in some way precipitated, by the atypical pneumonia agent M. pneumoniae has come to be viewed as a postinfectious immune disease, as discussed in Chap. 31. However, portions of the DNA from this organism have been found in the spinal fluid early in the course of illness in some cases, suggesting the possibility of a direct bacterial infection of the spinal cord. It is not known whether antibiotic treatment alters the course of the illness.
Syphilitic myelitis is also discussed in Chap. 31. Bacterial abscess of the spinal cord is rare, especially in comparison to epidural spinal abscess, and it is recognized by MRI. At times, it stands as a single pyogenic metastasis from a distant infection and subsequent bacteremia, but more often there has been spread from a contiguous infected surgical site or a fistulous connection with a superficial paraspinal abscess. Vertebral osteomyelitis is addressed further on in relation to epidural abscess.
Sarcoid Myelitis (See Also Sarcoidosis in Chap. 31)
Sarcoid granulomas may occur as one or more intramedullary spinal cord masses, as in the cases reported by Levivier and colleagues. In our experience, the granulomatous lesion, which may be focal or multifocal, simulates demyelinative disease with respect to its tendency to relapse and remit and in its response to corticosteroids. An asymmetrical ascending paraparesis and bladder disturbance have been the main features in our patients. Usually there is evidence of systemic sarcoidosis and the CSF is abnormal (increase in cells and protein; glucose usually normal), but we have encountered a few instances of sarcoid restricted to the spinal cord before it was evident in the mediastinum (i.e., thoracic CT failing to demonstrate hilar adenopathy or diffuse parenchymal lung disease). Elevation of the spinal fluid IgG concentration and oligoclonal bands may be found, but they are not consistent features; often there are activated histiocytes in the CSF.
The use of angiotensin-converting enzyme levels in the CSF to distinguish sarcoidosis from multiple sclerosis suffers from the lack of normative values for this test, but it is reported in some small series to be elevated in two-thirds of patients. The MRI is abnormal and the conus or other portions of the cord reveal intramedullary lesions. The most characteristic finding, however, is a multifocal-subpial nodular enhancement of the meninges adjacent to a lesion within the cord or nerve roots—a picture that resembles neoplastic meningeal infiltration. The diagnosis can be confirmed by mediastinal lymph node biopsy or by the far less desirable method of biopsy of the spinal meninges, spinal roots and affected subpial cord.
On occasion, a number of other rare granulomatous conditions cause an intrinsic or, more often, extrinsic compressive myelopathy; these, include brucellosis, xanthogranulomatosis, and eosinophilic granuloma. The diagnosis may be suspected if the systemic disease is apparent at the time but usually, only the histology of a surgical specimen reveals the underlying process.