Cerebrospinal Fluid HIV Escape Associated with Progressive Neurologic Dysfunction in Patients on Antiretroviral Therapy with Well-Controlled Plasma Viral Load

Abstract

Objective

To characterize HIV-infected patients with neuro-symptomatic CSF ‘escape,’ defined as detectable CSF HIV RNA in the setting of treatment-suppressed plasma levels or CSF RNA >1 log higher than plasma RNA.

Design

Retrospective case series.

Setting

4 urban medical centers in the United States and Europe.

Subjects

Virologically controlled HIV-infected patients on antiretroviral therapy (ART) with progressive neurologic abnormalities who were determined to have CSF ‘escape.’

Intervention

Optimization of ART based upon drug susceptibility and presumed CNS exposure.

Main outcome measures

Levels of CSF HIV RNA and inflammatory markers, clinical signs and symptoms, magnetic resonance imaging findings.

Results

10 patients presented with new neurological abnormalities, which included sensory, motor, and cognitive manifestations. Median CSF HIV RNA was 3900 copies/mL (range 134-9056), while median plasma HIV RNA was 62 copies/mL (range <50-380). Median CD4⁺ T cell count was 482 cells/mm³ (range, 290-660). All patients had been controlled <500 copies/mL for median 27.5 months (range, 2-96) and 5/10 had been suppressed <50 copies/mL for median 19.5 months (range, 2-96). Patients had documentation of a stable ART regimen for median 21 months (range 9-60). All had CSF pleocytosis or elevated CSF protein; 7/8 had abnormalities on MRI; and 6/7 harbored CSF resistance mutations. Following optimization of ART, 8/9 patients improved clinically.

Conclusions

The development of neurologic symptoms in patients on ART with low or undetectable plasma HIV levels may be an indication of CSF ‘escape.’ This study adds to a growing body of literature regarding this rare condition in well-controlled HIV infection.

Background

HIV-1 infection is present in the central nervous system (CNS) beginning during primary viremia and continuing over the course of untreated infection [1-3]. While most patients with HIV infection do not present with neurologic symptoms, elevated HIV RNA levels in the cerebrospinal fluid (CSF) can be associated with HIV encephalitis (HIVE) and HIV-associated dementia (HAD) in patients with advanced infection [4]. Antiretroviral therapy (ART) suppresses plasma and CSF viral levels and improves neurologic outcomes in patients with HIV [5]. As a result, the incidence of HAD has substantially decreased over the last two decades [6]. Additionally, even in asymptomatic patients, local HIV infection within the CNS may lead to distinct responses to ART in the neurologic and peripheral blood tissue compartments [7]. However, a subset of patients may still develop neurologic symptoms in the setting of long-term plasma viral control [8, 9].

Recently, Canestri et al. demonstrated the phenomenon of CSF/plasma HIV RNA discordance involving the development of new neurologic symptoms in eleven patients with well-controlled HIV [10]. In some cases, genotyping demonstrated significant resistance mutations in the CSF viral subpopulation, suggesting that the current treatment regimen had failed in the CNS. Some patients improved when their ART regimen was optimized based upon the results of genotyping and analysis of presumed CNS drug exposure.

We sought to add to the contributions of Canestri et al. and previous reports [11-15] by further investigating the condition of CSF ‘escape’ in patients will well-controlled plasma HIV and preserved immune function. One of the criticisms of previous reports has been that some patients have been on monotherapy [10] or salvage therapy [12, 13], and others have had low CD4⁺ T cell counts [10, 11]. We also sought to provide more detailed background information regarding HIV disease course in these patients and to emphasize key portions of the clinical picture, including neuroimaging, that have not been described in detail.

Here, we report a group of patients from four institutions in the United States and Europe. Each patient presented with new-onset neurologic symptoms in the context of low or undetectable plasma HIV levels, underwent neurologic studies including lumbar puncture and CSF analysis, and was noted to have CSF ‘escape.’ ART regimens were optimized based upon drug susceptibility and penetration. This study adds to a growing body of evidence regarding the rare condition of CSF ‘escape’ associated with progressive neurologic disease in otherwise well-controlled HIV infection.

Methods

Study Design and Patient Characteristics

We retrospectively compiled cases of HIV-infected patients on ART who presented with neurologic signs and/or symptoms in the context of plasma HIV RNA suppression and underwent evaluation including CSF studies. Subjects were identified at four urban academic centers in San Francisco, USA, Milan, Italy, New Haven, USA, and Gothenburg, Sweden.

All patients were on stable combination ART regimens with either suppressed (<500 copies/mL) or undetectable (<50 copies/mL) plasma HIV RNA. Patients with symptoms attributable to other neurologic or psychiatric causes were excluded. CSF and concurrent plasma samples were obtained either by the primary clinical team for diagnostic purposes or in the context of research studies in separate local protocols that were approved by the institutional review board or local equivalent at each institution. Clinical brain MRIs were obtained prior to lumbar puncture on varied local 1.5 Tesla scanners in the majority of subjects. We included patients found to have CSF ‘escape,’ defined as detectable CSF HIV RNA in the setting of plasma levels <50 copies/mL or CSF RNA >1 log higher than plasma RNA level as previously defined by Canestri and colleagues [10].

Laboratory Methods

HIV RNA levels were measured in cell-free CSF and plasma using the ultrasensitive Amplicor HIV Monitor (version 1.5; Roche Molecular Diagnostic Systems, Branchburg, NJ), Cobas TaqMan RealTime HIV-1 (version 1 or 2; Hoffmann-La Roche, Basel, Switzerland), or the Abbott RealTime HIV-1 (Abbot Laboratories, Abbot Park, IL, USA) assays at local sites. For uniformity, 50 copies/mL was used as the lower limit of quantitative detection in this analysis. Paired blood and CSF measurements used the same assay. CSF total WBC and protein, and CD4⁺ and CD8⁺ T lymphocyte counts by flow cytometry were measured at each local laboratory on fresh samples. Blood and CSF neopterin measurements employed commercially available immunoassays (BRAHMS Aktiengesellschaft, Hennigsdorf, Germany) and were performed in one laboratory. HIV resistance genotyping was performed where available in CSF samples harboring adequate HIV RNA levels for amplification. Genotyping was interpreted according to the International Antiviral Society-USA guidelines [16].

As a means to approximate expected effectiveness of ART in the CNS, we used proposed CNS penetration-effectiveness (CPE) scores using the 2010 version developed by Letendre and colleagues [18, 17] to calculate a “raw” CPE score for each regimen at the time when discordance was identified. In an effort to take into account effective resistance in a consistent, quantitative way, we calculated an “adjusted” CPE score based upon the genotyping results of CSF viral isolates. When a mutation to a particular drug in the regimen was identified, the individual CPE score for that drug was arbitrarily designated “0.”

Descriptive analyses were undertaken to characterize these patients and are reported as percentages or median value (range) for continuous variables.

Results

Between February 2000 and August 2011, 10 patients with chronic but well-controlled HIV infection and preserved immune status presented with new neurologic symptoms and were recognized as meeting the criteria for CSF ‘escape.’ The clinical and demographic characteristics of these patients are described in Table 1.

Table 1.

Demographic information and HIV history of patients with CSF/plasma discordance

		Historical Data				Time of Presentation
Site* Patient	Date of Presentation (month/year)	Age/Sex (years)	Nadir CD4+ T cell count (cells/mm3)	Documented time stable plasma HIV† (copies/mL: months)	CD4+ T cell count (cells/mm3)	Plasma HIV RNA (copies/mL)	Drug regimen	Neurologic Signs/Symptoms
SF 7066	02/2000	45/M	55	<50: n/a <500: 23	318	380	DDI SGC RTV	Cognitive impairment Gait ataxia
MI 9000	05/2003	46/F	15	<50: 28 <500: 28	305	372	3TC d4T LPV/r	Coma Tremor Vertigo
SF 1034	03/2004	51/M	80	<50: 2 <500: 2	588	<50	3TC ZDV LPV/r	Cognitive impairment Gait ataxia Tremor Weakness
SF 7071	07/2004	49/M	8	<50: 30 <500: 30	444	<50	3TC ZDV EFV LPV/r T-20	Cognitive impairment Gait ataxia Sensory impairment
SF 4065	02/2007	49/M	4	<50: 2 <500: 7	520	184	DDI TDF ATV/r	Cognitive Impairment Diplopia Dysarthria Dysphagia Gait ataxia
NH 2000	03/2007	55/M	60	<50: 96 <500: 96	308	<50	3TC ABC LPV/r	Aphasia Gait ataxia Sensory impairment Tremor Visual changes
GS 5168	05/2008	45/F	55	<50: 47 <500: 60	660	118	3TC TDF ATV/r	Cognitive impairment
MI 8000	08/2010	45/M	222	<50: 27 <500: 27	545	<50	3TC ABC FPV/r	Cognitive impairment Dysarthria Hyposthenia Sensory impairment Vertigo
MI 7000	01/2011	26/M	9	<50: 4 <500: 12	290	98	FTC TDF ATV	Diplopia Dysarthria Gait ataxia Headache Tremor
NH 1000	08/2011	49/M	180	<50: 12 <500: 43	627	<50	FTC TDF ATV/r RAL	Aphasia Cognitive impairment Gait ataxia Headache Tremor Vertigo

SF = San Francisco; MI = Milan, Italy; NH = New Haven; GS = Gothenburg, Sweden; n/a = not applicable

^*= site-specific research protocol identifiers are provided where available

^†= where <500 copies/mL is considered “good control” and <50 copies/mL is considered “undetectable,” length of time <500 copies/mL includes times when patient was <50 copies/mL; drug abbreviations: DDI = didanosine, SGC = saquinavir, RTV = ritonavir, 3TC = lamivudine , d4T = stavudine, LPV = lopinavir, ZDV = zidovudine, EFV = efavirenz, T-20 = enfuvirtide, TDF = tenofovir, ATV = atazanavir, ABC = abacavir, FPV = fosamprenavir, FTC = emtricitabine, RAL = raltegravir, /r = boosted with ritonavir.

The patients consisted of 8 men and 2 women with a median age of 47.5 years (range, 26-55 years). The median time since HIV diagnosis was 16.2 years (range, 9.4-21.7 years). At the time of the neurologic episode, the patients had been on a stable regimen for a median of 21 months (range, 9-60 months). These regimens consisted of at least 2 NRTIs plus a PI in 9/10 cases; the PI was boosted with ritonavir in 8/9 cases. Individual patients had additional components to their regimen, including integrase or fusion inhibitors. None were on mono- or dual-therapy.

The median duration of HIV RNA suppression below 500 copies was 27.5 months (range, 2-96 months). The median duration of HIV RNA suppression below 50 copies was 19.5 months (range, 2-96 months). The median CD4⁺ T cell count at presentation was 482 cells/mm³ (range, 290-660 cells/mm³). The median nadir CD4⁺ T cell count was 35 cells/mm³ (range, 4-222 cells/mm³).

Three patients had a previous neurologic abnormality. These included a presumed cerebellar meningioma that had been stable for many years (patient 1000), labyrinthitis and right sensorineural deafness (patient 8000), and CNS lymphoma that had resolved completely with initiation of ART, without radiotherapy, several years before (patient 5168).

Clinical and MRI Manifestations

The neurologic abnormalities present in this patient group (Table 1) occurred subacutely (>2 weeks) in 9/10 patients and were acute (<2 weeks) in 1 patient (patient 9000). They comprise a variety of sensory (in 3 patients), motor (in 9 patients), and cognitive (in 8 patients) manifestations. Imaging in 7/8 patients at the time of presentation showed MRI abnormalities consisting of white matter hyperintensities on T2-weighted and FLAIR sequences (table 2). Figure 1a-d shows representative imaging examples from patients 2000 and 7000 during the initial studies for neurologic symptoms.

Table 2.

Neurologic studies in patients with CSF/plasma discordance

		Cerebrospinal Fluid Analysis
Site Patient	Plasma HIV RNA (copies/mL)	HIV RNA (copies/mL)	Protein (mg/dL)	WBC (cells/mm3)	CSF Neopterin (nmol/L)	MRI Findings
SF 7066	380	9056	162	50	76.3	Not done
MI 9000	372	8000	170	0	-	Diffuse white matter abnormalities
SF 1034	<50	378	89	6	-	Patchy periventricular white matter abnormalities
SF 7071	<50	8320	60	33	-	Not done
SF 4065	184	4570	74	14	-	Patchy subcortical/ periventricular white matter abnormalities with involvement of corpus collosum and cerebellum
NH 2000	<50	613	77	28	-	Symmetric subcortical/ periventricular white matter abnormalities extending into cerebellum
GS 5168	118	3230	n/a	9	37.6	Slight deformity of frontal ventricular horns, stable compared to previous examinations. Otherwise normal.
MI 8000	<50	134	121	15	-	Diffuse white matter abnormalities
MI 7000	98	5200	137	200	-	Lenticular/posterior internal capsule/cingular cortex white matter abnormalities extending into cerebellum; diffuse pial contrast enhancement
NH 1000	<50	460	46	11	-	Cortical/subcortical/periventricular white matter abnormalities

WBC = white blood cells; SF = San Francisco; MI = Milan, Italy; NH = New Haven; GS = Gothenburg, Sweden; n/a = not available

Figure 1a-j. Selected MRI images for Patients 2000 and 7000.

Panels a-d show imaging at the time of neurologic workup when CSF ‘escape’ was detected for patients 2000 (a,b) and 7000 (c,d), demonstrating diffuse T2-prolongation (a,b) and suggesting focal lesions (d) at the time of CSF ‘escape.’ Panels e-h show follow-up imaging for patient 2000 at 111 days and patient 7000 at 60 days. Even though neurologic symptoms had resolved in both cases, imaging still shows diffuse leukoencephalopathy (e,f) and hyperintense, diffuse signal alteration of bilateral white matter (h), despite improvement of previous focal lesions (h). Panels i and j show imaging for patient 2000 at 567 days follow-up, demonstrating significant interval decrease in T2-prolongation.

CSF and Brain Pathology

CSF pleocytosis and biochemical abnormalities were found in all 10 patients (table 2). 8/9 patients had elevated CSF protein levels ≥ 60 mg/dL. The median protein level was 105 (range, 46-170). CSF pleocytosis was observed in 9/10 patients, with median 14.5 cells/mm³ (range 0-200 cells/mm³). All samples were negative for bacteria, fungi, and other viruses by standard microbiological tests at each institution, including JC virus DNA studies for progressive multifocal leukoencephalopathy (PML). Two samples (patients 1000 and 7000) had low-level (<5000 copies/mL) EBV DNA [18]. CSF from patient 5168 had previously been positive for EBV in the past when she suffered from CNS lymphoma, but CSF EBV titers were negative during and throughout the time of CSF HIV escape in this patient.

CSF neopterin was measured in two patients at the time of CSF ‘escape.’ Patient 7066 had a CSF neopterin level of 76.3 nmol/L with a plasma level of 12 nmol/L; patient 5168 had a CSF neopterin of 37.6 nmol/L with a plasma level of 8 nmol/L. Reference ranges for HIV-uninfected subjects are <5.8 nmol/L in CSF and <8.8 nmol/L in plasma [19]; for successfully ART-treated HIV-infected subjects, mean 10.8 nmol/L in CSF [20].

Two patients (1034 and 4065) underwent brain biopsy at the time of CSF ‘escape,’ revealing dense, perivascular lymphocytic infiltrates in the white matter with extension into the surrounding parenchyma. Immunoperoxidase staining showed a mixture of mature and immature B- and T-lymphocytes, with CD8⁺ predominance.

HIV RNA in CSF and Plasma

By definition, all patients had CSF HIV replication at initial evaluation, with a median of 3900 copies/mL (range, 134-9056 copies/mL). All had a plasma HIV RNA <500 copies/mL and 5/10 had a plasma HIV RNA <50 copies/mL at the time CSF ‘escape’ was discovered. The median plasma viral load was 62 copies/mL (range, <50-380 copies/mL). For the 5 patients with controlled but detectable plasma HIV RNA (>50 but <500 copies/mL), the CSF HIV RNA was at least 1 log higher than the plasma HIV RNA.

Figure 2 shows longitudinal plasma data for these patients, indicating plasma control <500 copies/mL in 7/10 patients over the previous 1000 days. Of these, 5/7 had HIV RNA below the limit of detection (<50 copies/mL) for the previous 1000 days. One patient had a transient increase in plasma viral load during this period (patient 4065), but had been well-controlled previously and following this increase. Two had viral loads that had more recently declined to <500 copies/mL (patients 1034 and 7000). These patients were included because they presented with new neurologic symptoms in the absence of alternate pathogens or focal lesions as determined through imaging or brain biopsy, with CSF ‘escape’ in the setting of preserved immune status and declining plasma HIV.

Figure 2. Longitudinal plasma HIV RNA levels for patients with CSF ‘escape’.

HIV RNA is calculated in days prior to time CSF/plasma discordance was detected (time “0”). Reference dotted horizontal line indicates log₁₀ 500 copies/mL. Corresponding CSF HIV RNA levels are indicated on the right axis of the graph at the time when CSF escape was identified (“CSF Escape”) and at a standardized follow-up timepoint, where repeat CSF was available (“Follow-up”).

Viral Resistance and CNS Penetration

Table 3 indicates the results of CNS genotyping and CNS penetration calculations. 6/7 patients on whom resistance gentoyping was conducted in the CSF had NRTI mutations, 5/7 patients had PI mutations, and 2/7 patients had NNRTI mutations. One patient had no mutations detected on CSF genotyping.

Table 3.

HIV drug regimens and resistance profiles in patients with CSF/plasma discordance

		Initial Regimen			New Regimen
Site Patient	Resistance Mutations Detected in CSF	Drugs in Regimen	Raw CPE	Adjusted CPE	Drugs in Regimen	Raw CPE	Adjusted CPE
SF 7066	Not done	DDI SGC RTV	3	n/a	ABC NVP IDV/r	11	n/a
MI 9000	NRTI: K65R, K70R, V75I, F77L, F116Y, Q151M, R211K NNRTI: none PI: I54V, A71V, V77I, V82F, L90M	3TC* d4T** LPV/r****	7	0	TDF* NVP APV/r T-20	9	8
SF 1034	Not done	3TC ZDV LPV/r	9	n/a	Not done	n/a	n/a
SF 7071	NRTI: D67N, T69D, K70R, L74V, T215F, K219Q NNRTI: V108I, Y181C, G190A, F227L PI: L10I, K20I, M36I, M46I, I50V, Q58E, L63P, A71V, L90M	3TC ZDV**** EFV*** LPV/r**** ** T-20	13	2	3TC TDF ZDV**** LPV/r**** ** T-20	11	4
SF 4065	NRTI: L74V, M184V, Y115F NNRTI: Y181C, F227L PI: L63P, A71T, V77I, I85V	DDI* TDF ATV/r**	3	1	3TC* ABC*** ZDV LPV/r*	12	4
NH 2000	NRTI: M41L, E44D, D67N, V118I, M184V, L210W, T215Y NNRTI: none PI: I13V, K20R, M36I, I54V, L63P, V82A	3TC* ABC* LPV/r****	5	0	3TC* ABC* ZDV* NVP DRV/r*	16	4
GS 5168	NRTI: M41L, V75A, M184I NNRTI: none PI: M36I, L63P	3TC* TDF ATV/r*	6	1	FTC* TDF DRV/r	7	4
MI 8000	Not done	3TC ABC FPV/r	8	n/a	3TC ABC ZDV FPV/r	12	n/a
MI 7000	NRTI: none NNRTI: none PI: none	FTC TDF ATV	9	9	3TC ZDV DRV/r	9	9
NH 1000	NRTI: M184I NNRTI: none PI: none	FTC* TDF ATV/r RAL	9	6	FTC* TDF ZDV ATV/r RAL	13	10

CPE = central nervous system penetration effectiveness; SF = San Francisco; MI = Milan, Italy; NH = New Haven; GS = Gothenburg, Sweden

^*denotes number of resistance mutations to each drug in regimen; n/a= not applicable; drug abbreviations: DDI = didanosine, SGC = saquinavir, RTV = ritonavir, 3TC = lamivudine , d4T = stavudine, LPV = lopinavir, ZDV = zidovudine, EFV = efavirenz, T-20 = enfuvirtide, TDF = tenofovir, ATV = atazanavir, ABC = abacavir, FPV = fosamprenavir, FTC = emtricitabine, RAL = raltegravir, NVP = nevirapine, IDV = indinavir, APV = amprenavir, DRV = darunavir, /r = boosted with ritonavir.

The original antiretroviral regimens for these patients had a median CPE score of 6.5 (range, 3-13). When adjusted for resistance, the median adjusted CPE score was 1 (range, 0-9). Regimens were revised in 9/10 subjects based on CSF findings. The revised regimens (see Table 3) had a median raw CPE score of 11 (range, 7-16) and median adjusted CPE score of 4 (range, 4-10).

Changes after Treatment Intervention

Eight out of nine patients demonstrated clinical improvement following neurologic evaluation and ART regimen optimization. One patient did not improve (patient 5168) and one patient died from septic shock secondary to presumed bowel ischemia before treatment was modified (patient 1034).

Follow-up CSF was available in 4/9 patients and demonstrated reduced CSF HIV RNA levels (from median 5775 copies/mL to median 66 copies/mL) at a median of 70 days following change in drug regimen (range, 11-189 days). In 3/4 cases, discordance between CSF and plasma resolved at this follow-up point; in 1 case, discordance persisted at a lower level (patient 5168 with 340 copies/mL in the CSF); this patient’s abnormalities did not improve after 189 days on the new regimen.

Figure 1e-h shows short-term follow-up imaging for patients 2000 and 7000. At 60 days, MRI for patient 7000 showed resolution of most focal lesions, but the development of a diffuse leukoencephalopathy despite resolution of symptoms. Similarly, patient 2000 had persistent diffuse white matter hyperintensities on MRI at 111 days, with subsequent significant decrease in these abnormalities at 346 and 567 days follow-up.

Discussion

We report 10 cases of elevated CSF HIV RNA in the setting of plasma suppression in patients with well-controlled HIV infection, with long-term plasma control and CD4⁺ T cell counts indicating preserved immune status at the time when neurologic symptoms developed. These cases demonstrate an unusual but clinically important phenomenon of CSF ‘escape’ associated with incident neurologic signs and symptoms in patients with chronic treated HIV infection.

The patients we report comprise a representative sample of those living with antiretroviral-treated HIV. This includes individuals with persistently suppressed plasma HIV RNA over many years (patient 2000), those who have been under control for a number of years (patients 1000, 7066, 7071, 9000, and 5168), those with good control but a recent ‘blip’ (patient 4065), and those with an unclear history who are coming under control (patients 1034 and 7000). The common clinical picture of neurologic abnormalities across this spectrum of patients suggests that the process of CSF ‘escape’ is a relevant consideration in a variety of clinical contexts.

Patients experienced a variety of neurologic symptoms including cognitive, sensory, and motor impairment. Onset was most often subacute, impairment varied in severity, and abnormalities progressed over time. Overall, the neurologic symptoms reflect a level of debilitation that was significant and involved a range of functional domains.

MRI findings were consistent among patients and with those reported in previous cases [10-12]. Furthermore, they are similar but not identical to those classically identified in typical HAD in patients off of ART. White matter hyperintensities on T2-weighted and FLAIR imaging suggest a generalized inflammatory process consistent with diffuse encephalitis, and similar to findings reported in patients failing ART [21]. Comparison of MRI results at the time of presentation (Figure 1a-d) and short and longterm follow-up (Figure 1e-h, 1i-j, respectively) suggests that this process is associated with findings on imaging that may persist after the resolution of symptoms, and may take months to years to resolve completely. Still, the nature of these imaging findings remains incompletely understood.

Despite relatively reconstituted immune status at the time of evaluation, all patients had CD4⁺ T cell nadirs <250 cells/mm³, with many below 100 cells/mm³, which is consistent with a previous report of a median nadir CD4⁺ T cell count of 55 cells/mm³ in similar patients [10]. A history of advanced immunosuppression may confer increased risk for prior enhanced local CNS infection and compartmentalization [22], which, despite peripheral CD4⁺ T cell improvement, fails to be entirely suppressed by ART. Clinically, the CD4⁺ T cell nadir might be an important factor to consider in the assessment of a patient with new neurologic abnormalities.

One concern with previously reported cases of CSF ‘escape’ has been that some patients have been on atypical or incomplete regimens [10]. No patients in our study were on mono- or dual-therapy. All were on appropriate multi-drug combination ART regimens before they developed symptoms, although some older regimens are outdated by current standards. Preserved immune status and suppression of plasma viremia suggest compliance with ART, though it cannot be ruled out that suboptimal adherence contributed. Theoretically, partially reduced adherence may lead to insufficient drug concentrations in the CSF while maintaining satisfactory concentrations in plasma. CSF drug concentrations may therefore be an important consideration in this subset of HIV patients, as has been suggested elsewhere [10]. CSF ‘escape’ may arise secondary to differences in susceptibility between HIV subpopulations in the blood and CSF [23-26] due to the selection of resistant virus in the context of sub-therapeutic drug levels in the CNS compartment [27].

While it has been argued that CNS drug penetration may be an important factor in the pathogenesis of CSF ‘escape’ [28], these cases indicate that viral resistance should also be considered. Resistance to at least one drug in the regimen was common. The “adjusted” CPE score represents a first attempt to incorporate resistance in a numerical calculation of drug effectiveness, and assumes that a single mutation will confer complete resistance to a drug, though, in fact, the drugs may remain partially effective despite the mutations. While it is unclear to what extent clinical improvement resulted from treatment interventions, most patients improved when their regimens were adjusted with regard to both penetration and resistance. This suggests that regimen modifications should be based on more than penetration alone.

Taken together, the range and quality of neurologic dysfunction and the MRI findings in these patients have substantial overlap with typical findings in HAD. However, despite this overlap, these are not identical to those in HAD and we believe that the etiology of these findings is slightly different than that of HAD in the absence of treatment. In accordance with previous reports [10-12], markedly elevated CSF total protein levels and white blood cell counts in our subjects compared to healthy HIV-uninfected controls and neuro-asymptomatic HIV-infected subjects on ‘successful’ ART [29] indicate a CNS inflammatory response. The pronounced inflammation/CD8⁺ T lymphocyte infiltration noted on brain biopsy in two patients suggests that CSF ‘escape’ in the setting of an immune system reconstituted by systemically successful ART is associated with a degree of local inflammation distinct from typical HAD/HIVE. CSF neopterin, which is elevated in HAD and reduced by ART [20, 30, 31], was markedly increased in comparison to plasma neopterin and typical values of CSF neopterin in HIV-infected, ART-suppressed subjects. This provides evidence that in cases of CSF ‘escape,’ inflammation may be relatively compartmentalized in the CNS. The role of inflammation in this disorder may determine the distinct neurotropism for these lesions, as reflected in MRI and clinical symptoms.

Given the observation that symptomatic CSF ‘escape’ is accompanied by CNS inflammation, a moderately reconstituted immune system may play an important role in both eliciting a symptomatic inflammatory response and in providing a substrate for ongoing discordant HIV replication within the CNS. Since all of the subjects had preserved immune function and none had recently initiated ART, typical immune reconstitution inflammatory syndrome (IRIS) was not considered the primary cause of these abnormalities. Nevertheless, the combination of persistent CNS infection and relatively preserved immune response, including an HIV-specific response, may generate immunopathology in cases of CSF ‘escape.’ This is analogous to IRIS [32], but may differ in that it represents not the effects of immune reconstitution, but rather a “stable state” of antigen and immune response within the CNS.

This analysis is limited by its retrospective approach, which utilized chart reviews and was constrained to studies previously performed during clinical evaluation and research protocols. It is unclear what the prevalence of CSF ‘escape’ may be in the general HIV-infected population, as patients with minor neurologic complaints are less likely to undergo detailed CNS evaluations. Our follow-up data are limited in many cases because further studies were not pursued once symptoms resolved.

Conclusions

Physicians should be aware of this unusual but clinically significant manifestation of HIV disease. These cases reflect that new neurologic symptoms in the context of standard ART regimens and well-controlled plasma HIV infection warrant an evaluation of the CSF to determine whether viral replication is occurring and, if so, whether the virus in the CSF compartment possesses resistance to the regimen being used to control the virus in the plasma compartment. CSF HIV analysis can be an important diagnostic tool and should be available to clinicians for the purpose of measuring HIV RNA concentration and identifying resistance. These cases add to the growing literature on CSF/plasma discordance that underscores the need for further investigation into the mechanism and consequences of HIV replication and persistence in the CNS.