Intramedullary spinal cord abscess (ISCA) is a rare central nervous system infection, associated with high mortality and neurological morbidity. The term "intramedullary" means "within the spinal cord." Thus, the term "intramedullary spinal cord abscess" may be redundant. As with epidural abscess, quick diagnosis and treatment of this condition are critical to the prevention of long-term serious damage to the spinal cord, or possibly death. Though we largely approach and treat these conditions similarly, we ought not to confuse ISCA with spinal epidural abscess, the latter of which is far more common.
The etiology of ISCA is primarily infectious. There are basically two ways that someone can acquire an infection of the parenchyma of the spinal cord: by hematological transport or by juxtaposition with infected tissue or cerebrospinal fluid. The sheath that surrounds the spinal cord (pia mater) comprises the inner lining of the central canal. It provides a layer of protection that contributes to the rarity of this condition. Though an ISCA is usually secondary to spinal cord epidural abscess, other etiologies have been observed. One example is that of aortic valve endocarditis.  In another case, an ISCA was associated with a spinal dural arteriovenous fistula, which was conducive to hematogenous infection of the spinal cord. 
Since Hart initially described the diagnosis in 1830, there have been at least 120 cases reported in the medical literature.  The age distribution for those with ISCA is bimodal, most commonly occurring in the first and third decades of life. Also, men are more commonly afflicted than women. It is uncertain whether this condition is more common in the United States than it is elsewhere in the world per capita, or whether some races are more likely to be afflicted by ISCA than others.
To remain viable, the spinal cord requires perfusion of its tissues with blood. When the pia mater is violated, or when a patient acquires an infection in the bloodstream, the pathogen may penetrate the blood-cord barrier. As a part of the central nervous system, the blood-cord barrier is functionally equivalent to the blood-brain barrier, leaving a certain segment of the population - especially those who are immunocompromised or intravenous drug users - at risk of developing an infection of the spinal cord due to mechanisms similar to those that may cause a brain abscess. 
Be sure to collect and history of infection, trauma, fever, or surgery of the thoracolumbar spine. The history may reveal that the patient has a condition that predisposes the patient either to the acquisition of virulent blood-borne pathogens, or immunosuppression such as due to diabetes, HIV positivity or glucocorticoid use. Note any exposure to intravenous routes of infection, such as by IV drug abuse. The history may also reveal trauma to the spinal cord, resulting in the violation of the pia mater, thereby compromising the blood-cord barrier. A local or systemic infection leading to ISCA may consist of spinal epidural abscess, vertebral osteomyelitis, or brain abscess.
On physical examination, take note of any motor or sensory deficits, and the myotomes and dermatomes at which they present, respectively. Consider the vital signs revealing fever, or laboratory values revealing leukocytosis, noting the low sensitivity of these values. Note lumbago local to the midline of the back, or that may be referred along a dermatome. Pain on palpation of the vertebra would not be likely in an ISCA, but it may suggest osteomyelitis, compression fracture, or malignancy. Regardless of the presence or abscess of back tenderness, further evaluation would be warranted considering other positive findings on history or examination.
Fever, leukocytosis, back pain, and focal neurological deficits should prompt an immediate radiographic evaluation using MRI with gadolinium of the spine. Also, take note of the loss of continence of bladder or bowel. Focal neurological deficits may come in the form of progressive lower-extremity paraparesis or saddle anesthesia. The probability that this constellation of symptoms would be due to spinal epidural abscess rather than ISCA is far greater. However, this workup may reveal that the patient does, in fact, have an ISCA. This ISCA may be solitary or multiple though it is usually solitary. It is typically located along the thoracic distribution though it can be located anywhere along the spinal cord.
Upon suspicion of ISCA, refer the patient to a neurologist. This specialist would consider whether to opt for surgical evacuation of the spinal cord abscess or not, or at least to pursue a biopsy of the pustulant abscess. They would investigate such a biopsy for Gram stain, culture, and sensitivity. A laminectomy may be required to get a biopsy. Empirical prescription and dispensation of antibiotics would be recommended as the team awaits laboratory results after which time more appropriate antibiotics may be administered. For this purpose, an infectious disease specialist may be consulted.
Ruling out spinal epidural abscess leads to the same workup for which we would rule out ISCA. Pott disease, osteomyelitis, compression fracture, diabetic neuropathy, or metastasis may also be differential diagnoses. Also, consider vascular etiologies such as spinal infarction due to spinal artery embolism. Monitor the progress that the patient makes following antiplatelet therapy to help distinguish between the two conditions.  The neurosurgeon will need a probable diagnosis to determine how biopsy or drainage should be attempted in the operating room.
Due to the advancement of medicine in the areas of antibiotics, radiology, and surgery, the mortality rate for ISCA has gone from 90% between 1840 and 1944 to 4% between 1998 and 2007.  Still, there is potential for neurological sequelae such as paralysis or sensory deficiency. These sequelae may be treated with physical medicine and rehabilitation.
Neurological PM&R may be helpful for those patients whose spinal cord abscesses have reduced their mobility or functionality. Though studies are not readily available detailing the extent to which PM&R can help those who suffer from this condition, we can infer its utility from studies that have shown its utility in helping those who have suffered from spinal cord injuries by other means.
Potential consultations may involve neurologists, neurosurgeons, infectious disease specialists, and physical medicine and rehabilitation doctors.
It is important for the physician who suspects ISCA to coordinate care with a neurologist, a neurosurgeon, an infectious disease specialist, and a PMNR specialist as required to rule out or treat this condition. As ISCA is limited to approximately 120 cases in the literature, it is a poorly studied condition. Thus, recommendations regarding diagnosis, treatment, and prognosis are mostly limited to Level V evidence. Due to the close kinship between the approach to the far-more-common spinal epidural abscess and that of ISCA, a good strategy would be to do what we would ordinarily do to rule out the former while being open to the possibility that the latter may be the culprit lesion.
The prognosis is good with prompt surgical treatment and antibiotics. However, the size, location of the abscess and severity of the neurological deficits determine the eventual outcome. Despite advances in treatment, spinal cord abscess still carries mortality in excess of 10%, and most patients are left with some type of residual neurological deficit. Recurrence of the abscess has been noted in most series and hence, repeat MRIs are needed during follow up.
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