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|Year : 2021 | Volume
| Issue : 2 | Page : 392-393
Recurrent Solitary Cysticercus Granuloma: Definition is Crucial
Department of Neurological Sciences, Christian Medical College Hospital, Vellore, Tamil Nadu, India
|Date of Submission||12-Oct-2020|
|Date of Decision||12-Oct-2020|
|Date of Acceptance||14-Oct-2020|
|Date of Web Publication||24-Apr-2021|
Department of Neurological Sciences, Christian Medical College Hospital, Vellore - 632 004, Tamil Nadu
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Rajshekhar V. Recurrent Solitary Cysticercus Granuloma: Definition is Crucial. Neurol India 2021;69:392-3
The authors of the article “Recurrent neurocysticercosis: not as rare” are to be congratulated for drawing the attention of clinicians to an important manifestation of a solitary cysticercus granuloma (SCG), namely the possibility of the granuloma to recur. A recurrent SCG can be mistaken for either a persistent lesion or worse still, can be mistaken for a tuberculoma. The latter error can lead to inappropriate and potentially toxic therapy with anti-tuberculous drugs or unnecessary brain surgery.
Recurrence of a solitary cysticercus granuloma (SCG) is uncommon, but the authors would like us to believe otherwise. They recorded a very high recurrence rate of 12.6% compared to 0% to 4% in several large series of patients with SCG. They attribute their high rate to their practice in a high volume tertiary care centre. But, why is it that other authors who also practice in similar locations reported low rates of recurrent SCG? To understand this variation in the reported incidence of recurrent SCG, we must analyse the possible pitfalls in the diagnosis of recurrent SCG and follow up biases.
The first step in ensuring uniformity in reporting this entity is to define it. The term “recurrence” in medical parlance is understood as occurrence of a disease or lesion after the initial manifestation of the disease or the initial lesion has regressed completely with a disease/lesion-free interval of time. Applying this meaning of “recurrence” to SCG, recurrent SCG would be defined as: “Occurrence of a SCG at the same or another location as a previously diagnosed SCG, which has been documented to have resolved”. The first reports of recurrent SCG which fulfilled this definition were published in 1999.,
Several cases reported by the authors do not fulfil the above mentioned definition of a recurrent SCG. Some cases would be labeled as “enlarging” SCG (Cases 2 and 3; [Figure 2]e, [Figure 2]f, [Figure 2]g, [Figure 2]h, [Figure 2]i). The entity of “enlarging” SCG has been documented and defined several years ago. Although, the authors have justified the inclusion of these cases in their series, they cannot be diagnosed as “recurrent” as the initial SCG has not resolved. At least two cases (Cases 5 and 11, [Figure 3]d, [Figure 3]f and [Figure 4]g, [Figure 4]h) appear to be persistent SCGs which were quiescent for several months or years and became inflamed, a phenomenon which is well recognized not only in SCG but also in calcified cysticercal granulomas.
Follow up biases can also lead to an overestimation of the incidence of recurrent SCG. In the authors' retrospective study, 159 of 278 patients who met the diagnostic criteria for SCG were excluded due to various reasons including lack of follow up. Patients with recurrent SCG are more likely to be symptomatic and are, therefore, more likely to come for follow up than those who are asymptomatic. This will lead to a higher incidence of patients with recurrent SCG.
In the 1980s, the commonest cause of misdiagnosis of “recurrent” SCG was misdiagnosing “resolution” of the initial granuloma on an inadequate neuroimaging such as a CT scan with thick slices (≥5 mm) or performed using a low resolution early generation CT scanner. Such scans will miss a small residue. In a prospective natural history study of 210 patients with SCG, 36% of patients with partial resolution of the granuloma on follow up imaging had residual lesions measuring ≤5 mm. So it is possible that the residual granuloma in these patients could have been missed if the slice thickness was ≥5 mm. In the authors' series this was not an issue as the initial SCG was visible on several scans in which “recurrence” was diagnosed.
The other imaging error is mistaking the location of the “recurrent” SCG to be adjacent to the initial SCG when in fact it is in the same location. Close comparison of the sulcal and gyral patterns in the vicinity of the initially diagnosed SCG and the “recurrent” one is the best method to avoid a misdiagnosis. Such misdiagnosis is more likely to occur when several months or years have passed since the initial diagnosis and the clinicians expect the initial lesion to have resolved.
The pathogenesis of recurrent SCG has been well discussed by the authors. Although they believe that “co-localization” of two cysts at the initial infection, to be the commonest cause of “recurrence”, this might be the cause of true recurrent cysts in only a few patients, while most others with “co-localized” cysts develop an “enlarging” SCG. Recurrence in this situation, can be diagnosed when the first cyst has either completely resolved without leaving a residue or has left a calcific residue and the second cyst, which was not visible on the initial imaging, starts degenerating and forms a granuloma, several weeks or months after the first cyst has resolved. The authors' proposed correlation between the imaging morphology and the degeneration of a single or two adjacent cysts is interesting but speculative.
The most common cause of a true recurrent SCG is likely to be re-infection of the patient as the patient is exposed to the same environment that led to the initial infection or infrequently if the patient is a taenia carrier he/she may have repeated bouts of auto-infection. There are two intriguing features to consider if recurrence is attributed to re-infection. First, the disease again manifests as a solitary cyst and second, the cyst lodges at the same site or close to the initial SCG. The former feature can be attributed to the host-parasite interaction and the latter to the angio-architecture of the cerebral vasculature which are unique to a given patient and hence lead to the same outcome with repeated infections.
Notwithstanding the overestimation of the incidence of recurrent SCG, the authors have done a service by increasing the awareness and recognition of this entity as it is crucial to the appropriate management of patients with SCG.
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