The "Claw Sign" may aid in axial localization in cases of peripherally located canine glioma on MRI.

The "claw sign" is a radiographic sign studied in human imaging to determine if a mass arises from a solid structure or organ versus a close adjacent location, resulting in distortion of the outline of an organ. We investigated its utility in characterizing MRI axial localization of peripherally located intracranial glioma versus meningioma, due to their overlap in MRI appearance. This retrospective, secondary analysis, cross-sectional study aimed to report the sensitivity, specificity, and inter- and intraobserver variabilities using kappa statistics, hypothesizing that the claw sign will have strong inter- and intraobserver agreement (κ > 0.8). Dogs with a histologically confirmed diagnosis of peripherally located glioma or meningioma and available 3T MRI data were retrieved from medical record archives from 2009 to 2021. A total of 27 cases, 11 glioma and 16 meningioma, were included. The postcontrast T1-weighted images were provided to five blinded image evaluators in two separate randomized sessions separated by a 6-week wash out period. Prior to the first evaluation, evaluators were provided with a training video and set of training cases for the "claw sign," which were excluded from the study. Evaluators were asked to rate cases as "positive," "negative," or "indeterminate" for the "claw sign." The sensitivity and specificity for the "claw sign" for the first session were 85.5% and 80%, respectively. The interobserver agreement for identifying the "claw sign" was moderate (κ = 0.48), and the intraobserver agreement across the two sessions was substantial (κ = 0.72). These findings indicate the claw sign is supportive but not pathognomonic for intra-axial localization in cases of canine glioma on MRI.

Cardiac Magnetic Resonance Imaging Detects Myocardial Abnormalities in Naturally Infected Dogs with Chronic Asymptomatic Chagas Disease.

Trypanosoma cruzi infection causes inflammation and fibrosis, resulting in cardiac damage in dogs. The objectives of this study were to describe cardiac magnetic resonance imaging (CMR) in naturally infected dogs with chronic Chagas disease and the frequency of abnormalities for CMR and cardiac diagnostic tests. Ten asymptomatic, client-owned dogs seropositive for T. cruzi were prospectively enrolled in an observational study evaluating echocardiography, ECG (standard and ambulatory), cardiac troponin I (cTnI), and CMR. Standard ECG measurements (3/10) and cTnI concentration (1/10) outside the reference range were uncommon. Ambulatory ECG abnormalities were documented more frequently (6/10 dogs) than with standard ECG and included ventricular arrhythmias (4), supraventricular premature beats (3), second-degree atrioventricular block (2), and sinus arrest (1). Echocardiographic abnormalities were documented in 6/10 dogs including mildly increased left ventricular internal dimension in diastole (1) and decreased right ventricular (RV) systolic function based on reductions in tricuspid annular plane systolic excursion (3) and RV S' (4). Abnormalities were detected with CMR in 7/10 dogs including delayed myocardial enhancement in 5 of which 2 also had increased extracellular volume, abnormal wall motion in 5, and loss of apical compact myocardium in 1. In conclusion, CMR abnormalities were common, and the results of this study suggest CMR can provide useful information in dogs with T. cruzi infection and may support naturally infected dogs for future clinical investigation as an animal model for Chagas disease.

Effect of withholding food versus feeding on creatinine, symmetric dimethylarginine, cholesterol, triglycerides, and other biochemical analytes in 100 healthy dogs.

BACKGROUND: Withholding food is often recommended before collection of blood for routine biochemical analysis in dogs despite a paucity of evidence to support this requirement. OBJECTIVES: To compare measurements of selected biochemical analytes collected before and after feeding in clinically healthy dogs. ANIMALS: One hundred clinically healthy staff- and student-owned dogs weighing ≥15 kg. METHODS: Prospective observational study. Food was withheld from the dogs for 10-26 hours. Preprandial serum was collected, and then dogs were fed their usual food at an amount equivalent to at least 2/3 resting energy requirement (RER). Selected serum analytes were measured at 2-, 4-, 6-, and 8-hours postprandially. The proportion of postprandial values that exceeded either the reported allowable total error (TEa), or for symmetric dimethylarginine (SDMA), the reference change value (RCV), was determined. As neither TEa nor RCV is available for lipase, comparison was made to the high end of the reference interval (RI). RESULTS: The proportion of dogs with at least 1 postprandial measurement that exceeded the TEa or RCV was 92/100 for triglycerides, 66/100 for blood urea nitrogen (BUN), 46/100 for phosphorus, 17/100 for glucose, 9/100 for bilirubin, 5/100 for SDMA, 2/100 for creatinine, and 0/100 for cholesterol and albumin. Postprandial lipase never exceeded the RI in dogs with normal fasted lipase. CONCLUSIONS AND CLINICAL IMPORTANCE: Withholding food is generally not necessary before performing routine biochemical analysis in clinically healthy dogs. Withholding food might be helpful to limit variability in analytes impacted by feeding, such as triglycerides and phosphorus.

Tralesinidase Alfa Enzyme Replacement Therapy Prevents Disease Manifestations in a Canine Model of Mucopolysaccharidosis Type IIIB.

Mucopolysaccharidosis type IIIB (MPS IIIB; Sanfilippo syndrome B; OMIM #252920) is a lethal, pediatric, neuropathic, autosomal recessive, and lysosomal storage disease with no approved therapy. Patients are deficient in the activity of N-acetyl-alpha-glucosaminidase (NAGLU; EC 3.2.150), necessary for normal lysosomal degradation of the glycosaminoglycan heparan sulfate (HS). Tralesinidase alfa (TA), a fusion protein comprised of recombinant human NAGLU and a modified human insulin-like growth factor 2, is in development as an enzyme replacement therapy that is administered via intracerebroventricular (ICV) infusion, thus circumventing the blood brain barrier. Previous studies have confirmed ICV infusion results in widespread distribution of TA throughout the brains of mice and nonhuman primates. We assessed the long-term tolerability, pharmacology, and clinical efficacy of TA in a canine model of MPS IIIB over a 20-month study. Long-term administration of TA was well tolerated as compared with administration of vehicle. TA was widely distributed across brain regions, which was confirmed in a follow-up 8-week pharmacokinetic/pharmacodynamic study. MPS IIIB dogs treated for up to 20 months had near-normal levels of HS and nonreducing ends of HS in cerebrospinal fluid and central nervous system (CNS) tissues. TA-treated MPS IIIB dogs performed better on cognitive tests and had improved CNS pathology and decreased cerebellar volume loss relative to vehicle-treated MPS IIIB dogs. These findings demonstrate the ability of TA to prevent or limit the biochemical, pathologic, and cognitive manifestations of canine MPS IIIB disease, thus providing support of its potential long-term tolerability and efficacy in MPS IIIB subjects. SIGNIFICANCE STATEMENT: This work illustrates the efficacy and tolerability of tralesinidase alfa as a potential therapeutic for patients with mucopolysaccharidosis type IIIB (MPS IIIB) by documenting that administration to the central nervous system of MPS IIIB dogs prevents the accumulation of disease-associated glycosaminoglycans in lysosomes, hepatomegaly, cerebellar atrophy, and cognitive decline.

Agreement and differentiation of intradural spinal cord lesions in dogs using magnetic resonance imaging.

BACKGROUND: Magnetic resonance imaging is the method of choice for diagnosing spinal cord neoplasia, but the accuracy of designating the relationship of a neoplasm to the meninges and agreement among observers is unknown. OBJECTIVES: To determine agreement among observers and accuracy of diagnosis compared with histology when diagnosing lesion location based on relationship to the meninges. ANIMALS: Magnetic resonance images from 53 dogs with intradural extramedullary and intramedullary spinal neoplasms and 17 dogs with degenerative myelopathy. METHODS: Six observers were supplied with 2 sets of 35 images at different time points and asked to designate lesion location. Agreement in each set was analyzed using kappa (κ) statistics. We tabulated total correct allocations and calculated sensitivity, specificity, and likelihood ratios for location designation from images compared with known histologic location for lesions confined to 1 location only. RESULTS: Agreement in the first set of images was moderate (κ = 0.51; 95% confidence interval [CI], 0.43-0.58) and in the second, substantial (κ = 0.69; 95% CI, 0.66-0.79). In the accuracy study, 180 (75%) of the 240 diagnostic calls were correct. Sensitivity and specificity were moderate to high for all compartments, except poor sensitivity was found for intradural extramedullary lesions. Positive likelihood ratios were high for intradural extramedullary lesions and degenerative myelopathy. CONCLUSIONS AND CLINICAL IMPORTANCE: Overall accuracy in diagnosis was reasonable, and positive diagnostic calls for intradural extramedullary lesions and negative calls for intramedullary lesions are likely to be helpful. Observers exhibited considerable disagreement in designation of lesions relationship to the meninges.

The impact of a surgical checklist on surgical outcomes in an academic institution.

OBJECTIVE: To determine the influence of a surgical checklist (SC) on morbidities and compliance with safety measures. STUDY DESIGN: Before-and-after-intervention study. SAMPLE POPULATION: Three thousand two hundred eighty-six dogs: 1375 dogs pre-SC and 1911 post-SC. METHODS: Completion of safety measures and occurrence of morbidity and/or mortality during hospitalization and up to death or 30-days postoperatively were recorded. RESULTS: Safety measures were more frequently completed post-SC, including oral confirmation of patient identity (467/1177 [40%] vs. 1911/1911 [100%]) and oral confirmation of surgical site (568/1175 [48%] vs. 1911/1911 [100%]). In addition, duration of anesthesia decreased from 241 to 232 min (t = 2.824; p = .005); a greater proportion of animals that were intended to receive antibiotics did so prior to incision (1142/1316 [86.8%] vs. 1656/1845 [89.8%] [χ2 = 6.70, p = .01]); and fewer dogs had unplanned return to the OR (32/1065 [3.0%], vs. 21/1472 [1.4%]) (χ2 = 7.52, p = .006). No difference in surgical site infection (adjusted odds ratio 1.02 [95%CI: 0.63-1.66]); morbidity, (adjusted odds ratio 1.00 [95%CI: 0.77-1.29]); or death within 30 days (adjusted odds ratio 1.15 [95%CI: 0.72-1.83]) was detected on multivariable logistic regression analysis. The checklist prevented one wrong-site surgery. CONCLUSION: Implementation of the checklist at our institution led to a decrease in anesthesia duration, increased administration of planned perioperative antibiotics before incision, increased completion of safety measures, and decreased unexpected return to the OR. IMPACT: Despite the lack of effect on morbidities, the use of SC is recommended to improve compliance with safety measures and potentially prevent rare catastrophic events.

An Analysis of Variability in "CatWalk" Locomotor Measurements to Aid Experimental Design and Interpretation.

Preclinical studies in models of neurologic injury and disease rely on behavioral outcomes to measure intervention efficacy. For spinal cord injury, the CatWalk system provides unbiased quantitative assessment of subtle aspects of locomotor function in rodents and so can powerfully detect significant differences between experimental and control groups. Although clearly of key importance, summary group-level data can obscure the variability within and between individual subjects and therefore make it difficult to understand the magnitude of effect in individual animals and the proportion of a group that may show benefit. Here, we calculate reference change intervals (RCIs) that define boundaries of normal variability for measures of rat locomotion on the CatWalk. Our results indicate that many commonly-used outcome measures are highly variable, such that differences of up to 70% from baseline value must be considered normal variation. Many CatWalk outcome variables are also highly correlated and dependent on run speed. Application of calculated RCIs to open access data (https://scicrunch.org/odc-sci) on hindlimb stride length in spinal cord-injured rats illustrates the complementarity between group-level (16 mm change; p = 0.0009) and individual-level (5/32 animals show change outside RCI boundaries) analysis between week 3 and week 6 after injury. We also conclude that interdependence among CatWalk variables implies that test "batteries" require careful composition to ensure that different aspects of defective gait are analyzed. Calculation of RCIs aids in experimental design by quantifying variability and enriches overall data analysis by providing details of change at an individual level that complement group-level analysis.

Electrodiagnostic findings in dogs with apparently painful lumbosacral foraminal stenosis.

BACKGROUND: Development of management strategies for lumbosacral stenosis in dogs is hampered by the lack of objective diagnostic criteria and outcome measures. OBJECTIVE: To explore the suitability of electrodiagnostic tests as ancillary diagnostic aids, inclusion criteria, or outcome measures. SAMPLE POPULATION: Sixty-one client-owned dogs with clinical signs of lumbosacral foraminal stenosis. METHODS: A blinded, cross-sectional cohort study. Fifty-one dogs exhibiting apparent lumbosacral pain or pelvic limb lameness with no detected orthopedic cause had blinded review of magnetic resonance imaging (MRI), allowing classification as affected with foraminal stenosis (25 dogs), unaffected (20 dogs), or another diagnosis (6 dogs). The presence of electromyographic changes and tibial neurography variables were compared between groups. RESULTS: Cord dorsum potential onset latency, F-wave onset latency (both corrected for limb length), and F-ratio were increased in dogs with lumbosacral foraminal stenosis versus those without, although there was overlap of the values between groups. The proportion of dogs with electromyographic changes was not significantly greater in MRI-affected dogs. CONCLUSION: Electrophysiological testing is a useful ancillary test, either to provide stricter inclusion criteria and outcome measures or to aid clinical decision-making in equivocal cases.

Surgical intervention for vertebral osteomyelitis in a calf.

OBJECTIVE: To report the surgical treatment and outcome of a non-ambulatory calf with cervical vertebral ostoeomyelitis. STUDY DESIGN: Clinical report. SAMPLE POPULATION: One 3.5-month-old female mixed-breed calf with tetraparesis of 3 months duration. METHODS: After computed tomography-guided bone biopsy, a bacterial osteolytic lesion within the body of the fourth cervical vertebrae (C4) and resultant pathologic compression fracture clinically resulting in full tetraparesis was diagnosed in the calf. Culture results from the lesion within C4 confirmed a diagnosis of Trueperella pyogenes. RESULTS: Poor response to medical management justified surgical debridment of the lesion in C4 and subsequent stabilization of the cervical vertebral column. A three-part procedure was performed including (1) debridement of the C4, (2) bilateral ventral vertebral stabilization from C3 to C5, and (3) placement of ampicillin-impregnated plaster of Paris beads within the body of C4. With postoperative physical rehabilitation, the calf regained full ambulatory function. At 1-month follow-up, the calf remained ambulatory with mild proprioceptive ataxia and no evidence of implant failure. At annual recheck, the calf had gained 208 kg and remained fully ambulatory with no residual neurologic deficits. CONCLUSION: Surgical intervention and use of antibiotic-impregnated implants offered a viable alternative to long-term medical management of vertebral osteomyelitis in the calf reported here. CLINICAL SIGNIFICANCE: This case identifies surgical intervention as a potential means for improving outcomes in a historically fatal condition of production animals.

A Wearable Body Controlling Device for Application of Functional Electrical Stimulation.

In this research, we describe a new balancing device used to stabilize the rear quarters of a patient dog with spinal cord injuries. Our approach uses inertial measurement sensing and direct leg actuation to lay a foundation for eventual muscle control by means of direct functional electrical stimulation (FES). During this phase of development, we designed and built a mechanical test-bed to develop the control and stimulation algorithms before we use the device on our animal subjects. We designed the bionic test-bed to mimic the typical walking gait of a dog and use it to develop and test the functionality of the balancing device for stabilization of patient dogs with hindquarter paralysis. We present analysis for various muscle stimulation and balancing strategies, and our device can be used by veterinarians to tailor the stimulation strength and temporal distribution for any individual patient dog. We develop stabilizing muscle stimulation strategies using the robotic test-bed to enhance walking stability. We present experimental results using the bionic test-bed to demonstrate that the balancing device can provide an effective sensing strategy and deliver the required motion control commands for stabilizing an actual dog with a spinal cord injury.

Comparison of Etomidate, Benzocaine, and MS222 Anesthesia with and without Subsequent Flunixin Meglumine Analgesia in African Clawed Frogs (Xenopus laevis).

Often few alternative anesthetics for exotic species are available, due to the small numbers of these animals used in research. In this study, we evaluated the depth and duration of anesthesia in Xenopus laevis after their immersion in 3 doses of etomidate (15, 22.5, and 30 mg/L) and in 3 doses of benzocaine (0.1%, 0.5%, and 1%) compared with the 'gold standard,' tricaine methanesulfonate (MS222; 2 g/L). We then chose an optimal dose for each alternative anesthetic according to induction time, duration of surgical plane, and time to complete recovery. The optimal etomidate and benzocaine doses (22.5 mg/L and 0.1%, respectively) as well as the MS222 dose were then used to achieve a surgical plane of anesthesia, with the addition of flunixin meglumine (25 or 50 mg/kg) administered in the dorsal lymph sac at the completion of mock oocyte harvest. Efficacy of the analgesic was assessed at 1, 3, 6, and 24 h postoperatively by using acetic acid testing (AAT). Histology of the liver, kidney, and tissues surrounding the dorsal lymph sac was performed at day 3, 14, and 28 in each group of animals. Mild to moderate myocyte degeneration and necrosis were present in tissues surrounding the dorsal lymph sac at both flunixin meglumine doses after etomidate and benzocaine anesthesia. In addition, the 50-mg/kg dose of flunixin meglumine resulted in the death of 5 of the 12 frogs within 24 h, despite an otherwise uneventful anesthetic recovery. In conclusion, benzocaine and etomidate offer alternative anesthetic regimens, according to typical requirements for an anesthetic event. Flunixin meglumine at the 25-mg/kg dose provided analgesic relief at the latest time point during etomidate dosage and at all time points during benzocaine dosage, but further characterization is warranted regarding long-term or repeated analgesic administration.

An ovine model of spinal cord injury.

OBJECTIVE: To develop a large animal model of spinal cord injury (SCI), for use in translational studies of spinal cord stimulation (SCS) in the treatment of spasticity. We seek to establish thresholds for the SCS parameters associated with reduction of post-SCI spasticity in the pelvic limbs, with implications for patients. STUDY DESIGN: The weight-drop method was used to create a moderate SCI in adult sheep, leading to mild spasticity in the pelvic limbs. Electrodes for electromyography (EMG) and an epidural spinal cord stimulator were then implanted. Behavioral and electrophysiological data were taken during treadmill ambulation in six animals, and in one animal with and without SCS at 0.1, 0.3, 0.5, and 0.9 V. SETTING: All surgical procedures were carried out at the University of Iowa. The gait measurements were made at Iowa State University. MATERIAL AND METHODS: Nine adult female sheep were used in these institutionally approved protocols. Six of them were trained in treadmill ambulation prior to SCI surgeries, and underwent gait analysis pre- and post-SCI. Stretch reflex and H-reflex measurements were also made in conscious animals. RESULTS: Gait analysis revealed repeatable quantitative differences in 20% of the key kinematic parameters of the sheep, pre- and post-SCI. Hock joint angular velocity increased toward the normal pre-injury baseline in the animal with SCS at 0.9 V. CONCLUSION: The ovine model is workable as a large animal surrogate suitable for translational studies of novel SCS therapies aimed at relieving spasticity in patients with SCI.

Perspectives on meningoencephalomyelitis of unknown origin.

Meningoencephalomyelitis of unknown origin (MUO) is a heterogeneous group of overlapping central nervous system inflammatory diseases of unknown cause. This article highlights the current understanding of MUO and its phenotypic variants encountered in clinical practice. Diagnostic evaluation of presumptive MUO includes lesion distribution on magnetic resonance imaging and ruling out other acquired diseases. Recent evidence provides further knowledge of immune-mediated processes that underlie the pathogenesis of MUO. Current empiric treatment options include corticosteroids and other adjunctive immunomodulating therapies. As the understanding of neuroimmunology and genetic influences on these disorders evolves, a more targeted treatment approach is becoming attainable.

Corticosteroid use in small animal neurology.

Glucocorticoid drugs are frequently used nonspecifically by veterinarians to control clinical signs associated with central nervous system disease. However, this use is infrequently justified and can also be associated with detrimental long-term patient outcomes. First, there are few diseases for which glucocorticoids are the preferred or definitive treatment. Second, their actions may blunt subsequent diagnostic efforts, for instance, by altering MRI appearance or cerebrospinal fluid cell content, or lead owners to abandon pursuit of more appropriate therapies if they perceive the first-line steroid therapy to be a failure.

Intracranial somatosensory responses with direct spinal cord stimulation in anesthetized sheep.

The efficacy of spinal cord stimulators is dependent on the ability of the device to functionally activate targeted structures within the spinal cord, while avoiding activation of near-by non-targeted structures. In theory, these objectives can best be achieved by delivering electrical stimuli directly to the surface of the spinal cord. The current experiments were performed to study the influence of different stimulating electrode positions on patterns of spinal cord electrophysiological activation. A custom-designed spinal cord neurostimulator was used to investigate the effects of lead position and stimulus amplitude on cortical electrophysiological responses to spinal cord stimulation. Brain recordings were obtained from subdural grids placed in four adult sheep. We systematically varied the position of the stimulating lead relative to the spinal cord and the voltage delivered by the device at each position, and then examined how these variables influenced cortical responses. A clear relationship was observed between voltage and electrode position, and the magnitude of high gamma-band oscillations. Direct stimulation of the dorsal column contralateral to the grid required the lowest voltage to evoke brain responses to spinal cord stimulation. Given the lower voltage thresholds associated with direct stimulation of the dorsal column, and its possible impact on the therapeutic window, this intradural modality may have particular clinical advantages over standard epidural techniques now in routine use.

Ovine tests of a novel spinal cord neuromodulator and dentate ligament fixation method.

BACKGROUND: To improve methods for the treatment of intractable pain, we are developing a novel intradural spinal cord stimulator that could be either attached to the dentate ligaments of the human spinal cord or fitted around the dorsal arc of the cord itself. PURPOSE: Our goal was to carry out the first in vivo tests of these attachment methods in an ovine model using custom-built devices and instrumentation. For eventual translational studies, we also explored methods of mimicking a human dentate ligament attachment technique in this large animal model. METHODS: As a starting point, we investigated details of the gross and histological anatomy of the ovine denticulate ligaments, and compared them with their human counterpart. The gap between the dura and the spinal cord in the sheep is small; hence, the denticulate ligaments are not long enough to accommodate human-scaled attachment clips. Therefore, lateral strips of the spinal-canal dura were fashioned to serve this same device attachment function. RESULTS: This form of dural anchoring was implemented surgically for fixation of a silicone membrane implant that had 12 electrodes, and somatosensory evoked potentials were obtained successfully when stimuli were applied to it. The dorsal arc clamping technique was also implemented. CONCLUSIONS: We demonstrated that the dural attachment method is an effective surrogate model for testing the human dentate ligament device fixation technique, and that this mode of fixation was preferable to dorsal arc attachment. The relevant surgical innovations, anatomical findings, and the preliminary electrophysiological data from a pial surface stimulator attached in this way are presented.

A new device concept for directly modulating spinal cord pathways: initial in vivo experimental results.

We describe a novel spinal cord (SC) stimulator that is designed to overcome a major shortcoming of existing stimulator devices: their restricted capacity to selectively activate targeted axons within the dorsal columns. This device overcomes that limitation by delivering electrical stimuli directly to the pial surface of the SC. Our goal in testing this device was to measure its ability to physiologically activate the SC and examine its capacity to modulate somatosensory evoked potentials (SSEPs) triggered by peripheral stimulation. In this acute study on adult sheep (n = 7), local field potentials were recorded from a grid placed in the subdural space of the right hemisphere during electrical stimulation of the left tibial nerve and the spinal cord. Large amplitude SSEPs (>200 µV) in response to SC stimulation were consistently obtained at stimulation strengths well below the thresholds inducing neural injury. Moreover, stimulation of the dorsal columns with signals employed routinely by devices in standard clinical use, e.g., 50 Hz, 0.2 ms pulse width, produced long-lasting changes (>4.5 h) in the SSEP patterns produced by subsequent tibial nerve stimulation. The results of these acute experiments demonstrate that this device can be safely secured to the SC surface and effectively activate somatosensory pathways.

Quantification of deficits in lateral paw positioning after spinal cord injury in dogs.

BACKGROUND: Previous analysis of the behavioural effects of spinal cord injury has focussed on coordination in the sagittal plane of movement between joints, limb girdle pairs or thoracic and pelvic limb pairs. In this study we extend the functional analysis of the consequences of clinical thoracolumbar spinal cord injury in dogs to quantify the well-recognised deficits in lateral stability during locomotion. Dogs have a high centre of mass thereby facilitating recognition of lateral instability. RESULTS: We confirm that errors in lateral positioning of the pelvic limb paws can be quantified and that there is a highly significant difference in variability of foot placement between normal and spinal cord injured dogs. In this study there was no detectable difference in lateral paw positioning variability between complete and incomplete injuries, but it appears that intergirdle limb coordination and appropriate lateral paw placement recover independently from one another. CONCLUSION: Analysis of lateral paw position in the dog provides an additional tier of analysis of outcome after spinal cord injury that will be of great value in interpreting the effects of putative therapeutic interventions.