Clinical Reasoning: A 32-Year-Old Woman With Tunnel Vision and Back Pain.

The incidence of new onset visual disturbances in emergency departments across the country is frequent. A detailed history of events and thoughtful physical examination may produce a diagnosis; however, atypical cases may require further diagnostic testing to explain symptoms. We present a case of presumed increased intracranial pressure with atypical findings on diagnostic testing, which allowed our team to explore a broader differential diagnosis. This clinical reasoning article will benefit students, residents, and attendings alike to continue to uncover etiologies for symptoms of increased intracranial pressure and review differential diagnoses in similar presentations.

Sex Differences in Tolerance to Delta-9-Tetrahydrocannabinol in Mice With Cisplatin-Evoked Chronic Neuropathic Pain.

Tolerance to the pain-relieving effects of cannabinoids limits the therapeutic potential of these drugs in patients with chronic pain. Recent preclinical research with rodents and clinical studies in humans has suggested important differences between males and females in the development of tolerance to cannabinoids. Our previous work found that male mice expressing a desensitization resistant form (S426A/S430A) of the type 1 cannabinoid receptor (CB1R) show delayed tolerance and increased sensitivity to the antinociceptive effects of delta-9-tetrahydrocannabinol (∆9-THC). Sex differences in tolerance have been reported in rodent models with females acquiring tolerance to ∆9-THC faster than males. However, it remains unknown whether the S426A/S430A mutation alters analgesic tolerance to ∆9-THC in mice with chemotherapy-evoked chronic neuropathic pain, and also whether this tolerance might be different between males and females. Male and female S426A/S430A mutant and wild-type littermates were made neuropathic using four once-weekly injections of 5 mg/kg cisplatin and subsequently assessed for tolerance to the anti-allodynic effects of 6 and/or 10 mg/kg ∆9-THC. Females acquired tolerance to the anti-allodynic effects of both 6 and 10 mg/kg ∆9-THC faster than males. In contrast, the S426A/S430A mutation did not alter tolerance to ∆9-THC in either male or female mice. The anti-allodynic effects of ∆9-THC were blocked following pretreatment with the CB1R antagonist, rimonabant, and partially blocked following pretreatment with the CB2R inverse agonist, SR144528. Our results show that disruption of the GRK/ß-arrestin-2 pathway of desensitization did not affect sensitivity and/or tolerance to ∆9-THC in a chronic pain model of neuropathy.

Safe Placement of Ommaya Reservoirs in Thrombocytopenic Patients: One Institutions Experience.

Objective The purpose of this study was to assess the risk of hemorrhagic complications in thrombocytopenic patients after Ommaya reservoir placement. Methods Between 2009 and 2017, 192 patients were identified on the National Neoplastic Meningitis Registry and had undergone Ommaya reservoir placement for intrathecal chemotherapy. A retrospective chart review was performed to collect the preoperative and postoperative platelet levels, whether or not the patient received any transfusion of platelets, neurological exams, and whether a postoperative head CT was obtained. Using generally accepted recommendations, a platelet level less than 100,000/µL was considered clinically significant and used as our threshold for thrombocytopenia. Results Seven patients (3.6%) were identified as thrombocytopenic in our patient population with platelet counts ranging from 54,000 to 99,000/µL. Primary diagnoses for the seven patients included leukemia, prostate cancer, primary brain cancer (four patients), and lung cancer (non-small-cell lung carcinoma). One patient received platelet transfusions preoperatively. Three patients had a routine head CT obtained postoperatively with no abnormal findings noted. There were no changes in the neurological exam noted in all of the patients included in this study. No clinically significant hemorrhages were identified in our patients. Conclusions From our single institutional experience, we found that thrombocytopenia is fairly uncommon, found in only 3.6% of our patients undergoing placement of Ommaya reservoirs. We did not encounter any increased risks of postoperative hemorrhage in studied thrombocytopenic patients.

Tolerance to WIN55,212-2 is delayed in desensitization-resistant S426A/S430A mice.

Tolerance to cannabinoid agonists can develop through desensitization of the cannabinoid receptor 1 (CB1) following prolonged administration. Desensitization results from phosphorylation of CB1 by a G protein-coupled receptor kinase (GRK), and subsequent association of the receptor with arrestin. Mice expressing a mutant form of CB1, in which the serine residues at two putative phosphorylation sites necessary for desensitization have been replaced by non-phosphorylatable alanines (S426A/S430A), display reduced tolerance to Δ9-tetrahydrocannabinol (Δ9-THC). Tolerance to the antinociceptive effects of WIN55,212-2 was delayed in S426A/S430A mutants using the tail-flick and formalin tests. However, tolerance to the antinociceptive effects of once daily CP55,940 injections was not significantly delayed in S426A/S430A mutant mice using either of these tests. Interestingly, the dose response curve shifts for the hypothermic and antinociceptive effects of CP55,940 that were induced by chronic treatment with this agonist in wild-type mice were blocked in S426A/S430A mutant mice. Assessment of mechanical allodynia in mice exhibiting chronic cisplatin-evoked neuropathic pain found that tolerance to the anti-allodynic effects WIN55,212-2 but not CP55,940 was delayed in S426A/S430A mice compared to wild-type littermates. Despite these deficits in tolerance, S426A/S430A mutant mice eventually developed tolerance to both WIN55,212-2 and CP55,940 for all pain assays that were examined, suggesting that other mechanisms likely contribute to tolerance for these cannabinoid agonists. These findings suggest that GRK- and ßarrestin2-mediated desensitization of CB1 may strongly contribute to the rate of tolerance to the antinociceptive effects of WIN55,212-2, and raises the possibility of agonist-specific mechanisms of cannabinoid tolerance.

Anti-nociceptive interactions between opioids and a cannabinoid receptor 2 agonist in inflammatory pain.

The cannabinoid 1 receptor and cannabinoid 2 receptor can both be targeted in the treatment of pain; yet, they have some important differences. Cannabinoid 1 receptor is expressed at high levels in the central nervous system, whereas cannabinoid 2 receptor is found predominantly, although not exclusively, outside the central nervous system. The objective of this study was to investigate potential interactions between cannabinoid 2 receptor and the mu-opioid receptor in pathological pain. The low level of adverse side effects and lack of tolerance for cannabinoid 2 receptor agonists are attractive pharmacotherapeutic traits. This study assessed the anti-nociceptive effects of a selective cannabinoid 2 receptor agonist (JWH-133) in pathological pain using mice subjected to inflammatory pain using the formalin test. Furthermore, we examined several ways in which JWH-133 may interact with morphine. JWH-133 produces dose-dependent anti-nociception during both the acute and inflammatory phases of the formalin test. This was observed in both male and female mice. However, a maximally efficacious dose of JWH-133 (1 mg/kg) was not associated with somatic withdrawal symptoms, motor impairment, or hypothermia. After eleven once-daily injections of 1 mg/JWH-133, no tolerance was observed in the formalin test. Cross-tolerance for the anti-nociceptive effects of JWH-133 and morphine were assessed to gain insight into physiologically relevant cannabinoid 2 receptor and mu-opioid receptor interaction. Mice made tolerant to the effects of morphine exhibited a lower JWH-133 response in both phases of the formalin test compared to vehicle-treated morphine-naïve animals. However, repeated daily JWH-133 administration did not cause cross-tolerance for morphine, suggesting opioid and cannabinoid 2 receptor cross-tolerance is unidirectional. However, preliminary data suggest co-administration of JWH-133 with morphine modestly attenuates morphine tolerance. Isobolographic analysis revealed that co-administration of JWH-133 and morphine has an additive effect on anti-nociception in the formalin test. Overall these findings show that cannabinoid 2 receptor may functionally interact with mu-opioid receptor to modulate anti-nociception in the formalin test.