Biomedical subjects

Dirk R Larson

Publications and source records attributed to Dirk R Larson.

45 records · Page 3Linked to original sources

PubMed2003

Biomechanical evaluation of new posterior occipitocervical instrumentation system.

Twelve fresh-frozen cadaveric occipitocervical specimens were randomized based on dual energy xray absorptiometry analysis of bone mineral density. The specimens were subjected to physiologic loads in a device that applied pure unconstrained flexion and extension, lateral bending, and axial rotational moments. The spines were tested intact and after major injury simulating transoral decompression of the dens. Biomechanical testing using pure moments with physiologic loads (< 1.5 N-m) was used to compare stability of posterior occipitocervical plates and screws, loop and cable construct, and new cervical rod and screw system. The injury created significantly less stiffness and greater range of motion and neutral zone at C1-C2 in flexion and extension and lateral bending and greater range of motion and neutral zone in axial rotation than the intact state. In lateral bending, the new rod construct had significantly lower mean values for range of motion than the loop and the plate construct. In axial rotation, the rod construct had a significantly higher mean value for stiffness than the other two devices and a significantly lower mean value for range of motion than the loop. The new rod-based instrumentation system for occipitocervical fixation is biomechanically equivalent or superior to a plate and screw construct and a rod and cable system.

Absorptiometry, Photon↗

PubMed2003

Primary (AL) hepatic amyloidosis: clinical features and natural history in 98 patients.

The liver is a common site of amyloid deposition in primary systemic amyloidosis. We reviewed the clinical features and natural history of patients with primary systemic amyloidosis and biopsy-proven hepatic involvement who were evaluated at Mayo Clinic from January 1, 1975, to December 31, 1997. The median age of the study group (68 men; 30 women) was 58.5 years. Seventy-one patients (72%) had involuntary weight loss. Hepatomegaly was found in 79 patients (81%). Eighty-two patients (89%) had proteinuria, and 81 patients (86%) had elevated serum alkaline phosphatase levels. Seventy-six patients (83%) had either a serum or urine monoclonal protein. Before liver biopsy, clinicians considered amyloidosis in the differential diagnosis for only 14 patients (26%). None of our patients experienced hepatic rupture or death due to liver biopsy, and only 4 (4%) bled after liver biopsy. The median survival of the 98 patients was 8.5 months. Predictors of a poor prognosis were congestive heart failure, elevated concentrations of bilirubin, and a platelet count greater than 500 x 109/L. In conclusion, clinicians should consider the diagnosis of primary hepatic amyloidosis in patients who present with involuntary weight loss or hepatomegaly. Other clues to the diagnosis include an unexplained elevated serum alkaline phosphatase level, proteinuria, and evidence for hyposplenism (for example, Howell-Jolly bodies on peripheral blood smear). Liver biopsy was safe. Some patients benefit from systemic chemotherapy.

Amyloidosis↗

PubMed2003

Review of 1027 patients with newly diagnosed multiple myeloma.

OBJECTIVE: To determine the clinical and laboratory features of newly diagnosed multiple myeloma. PATIENTS AND METHODS: Records of all patients in whom multiple myeloma was initially diagnosed at the Mayo Clinic in Rochester, Minn, from January 1, 1985, to December 31, 1998, were reviewed. RESULTS: Of the 1027 study patients, 2% were younger than 40 years, and 38% were 70 years or older. The median age was 66 years. Anemia was present initially in 73% of patients, hypercalcemia (calcium level > or = 11 mg/dL) in 13%, and a serum creatinine level of 2 mg/dL or more in 19%. The beta2-microglobulin level was increased in 75%. Serum protein electrophoresis revealed a localized band in 82% of patients, and immunoelectrophoresis or immunofixation showed a monoclonal protein in 93%. A monoclonal light chain was found in the urine in 78%. Nonsecretory myeloma was recognized in 3% of patients, whereas light-chain myeloma was present in 20%. Conventional radiographs showed an abnormality in 79%. The plasma cell labeling index was 1% or more in 34% of patients. Multivariate analysis revealed that age, plasma cell labeling index, low platelet count, serum albumin value, and the log of the creatinine value were the most important prognostic factors. CONCLUSION: The median duration of survival was 33 months and did not improve from 1985 through 1998.

Adult↗

PubMed2002

POEMS syndrome: definitions and long-term outcome.

The POEMS syndrome (coined to refer to polyneuropathy, organomegaly, endocrinopathy, M protein, and skin changes) remains poorly understood. Ambiguity exists over the features necessary to establish the diagnosis, treatment efficacy, and prognosis. We identified 99 patients with POEMS syndrome. Minimal criteria were a sensorimotor peripheral neuropathy and evidence of a monoclonal plasmaproliferative disorder. To distinguish POEMS from neuropathy associated with monoclonal gammopathy of undetermined significance, additional criteria were included: a bone lesion, Castleman disease, organomegaly (or lymphadenopathy), endocrinopathy, edema (peripheral edema, ascites, or effusions), and skin changes. The median age at presentation was 51 years; 63% were men. Median survival was 165 months. With the exception of fingernail clubbing (P =.03) and extravascular volume overload (P =.04), no presenting feature, including the number of presenting features, was predictive of survival. Response to therapy (P <.001) was predictive of survival. Pulmonary hypertension, renal failure, thrombotic events, and congestive heart failure were observed and appear to be part of the syndrome. In 18 patients (18%), new disease manifestations developed over time. More than 50% of patients had a response to radiation, and 22% to 50% had responses to prednisone and a combination of melphalan and prednisone, respectively. We conclude that the median survival of patients with POEMS syndrome is 165 months, independent of the number of syndrome features, bone lesions, or plasma cells at diagnosis. Additional features of the syndrome often develop, but the complications of classic multiple myeloma rarely develop.

Adult↗

PubMed2002

A long-term study of prognosis in monoclonal gammopathy of undetermined significance.

BACKGROUND: A monoclonal gammopathy of undetermined significance (MGUS) occurs in up to 2 percent of persons 50 years of age or older. Reliable predictors of progression have not been identified, and information on prognosis is limited. METHODS: We identified 1384 patients residing in southeastern Minnesota in whom MGUS was diagnosed at the Mayo Clinic from 1960 through 1994. The primary end point was progression to multiple myeloma or another plasma-cell cancer. RESULTS: During 11,009 person-years of follow-up, MGUS progressed in 115 of the 1384 patients to multiple myeloma, IgM lymphoma, primary amyloidosis, macroglobulinemia, chronic lymphocytic leukemia, or plasmacytoma (relative risk of progression, 25.0, 2.4, 8.4, 46.0, 0.9, and 8.5, respectively). The overall relative risk of progression was 7.3 in these patients as compared with the white population of the Iowa Surveillance, Epidemiology, and End Results program. In 32 additional patients, the monoclonal protein concentration increased to more than 3 g per deciliter or the percentage of plasma cells in the bone marrow increased to more than 10 percent (smoldering multiple myeloma) but without progression to overt myeloma or related disorders. The cumulative probability of progression was 12 percent at 10 years, 25 percent at 20 years, and 30 percent at 25 years. The initial concentration of serum monoclonal protein was a significant predictor of progression at 20 years. CONCLUSIONS: The risk of progression of MGUS to multiple myeloma or related disorders is about 1 percent per year.

Adult↗

PubMed2002

The Mayo Clinic experience with multimodality treatment of locally advanced or recurrent colon cancer.

BACKGROUND: Patients with incompletely resected locally advanced and recurrent colon cancers have a dismal prognosis. Since 1981, 100 colon cancer patients have been treated with combination therapy including surgical resection, chemotherapy, and external plus intraoperative radiotherapy. METHODS: A prospective computerized intraoperative radiation database identified patients for this retrospective review. Data collection included patient demographics, tumor and treatment variables, and morbidity, recurrence, and survival statistics. RESULTS: The mean age was 55.2 years. Follow-up was available for all patients. Fifty-nine patients have died. Median follow-up of survivors was 70.5 months. Twenty-five patients with locally advanced colon cancer had a median survival of 38.2 months and a 5-year survival of 49%. Eleven of these patients are still free of disease. Seventy-three patients treated for recurrent colon carcinoma had a median survival of 33.3 months from the time of recurrence, with a 5-year survival of 24.7%. Twenty-one are alive without evidence of recurrence. The 38 patients with recurrent disease whose disease was completely resected had a 37.4% 5-year survival. CONCLUSIONS: A multimodality approach using en-bloc surgical resection with radiotherapy and chemotherapy affords some patients with locally advanced and recurrent colon cancer a chance for long-term survival.

Adult↗

PubMed2002

Risk of lymph node metastasis in T1 carcinoma of the colon and rectum.

PURPOSE: Several recent reports of high local recurrence and lymph node metastasis in T1 carcinoma of the rectum prompted us to study the risk factors for lymph node metastasis in these lesions. METHODS: We reviewed the clinical records of 7,543 patients who underwent operative treatment for carcinoma of the colon and rectum from 1979 to 1995. Only patients with sessile T1 lesions who underwent colorectal resection were included in the study, yielding an analysis cohort of 353 patients. The following carcinoma-related variables were assessed: size, mucinous subtype, carcinomatous component, grade, site in colon and rectum, lymphovascular invasion, and depth of submucosal invasion. For the depth, the submucosa was divided into upper third (sm1), middle third (sm2), and lower third (sm3). Chi-squared tests and logistic regression were used to evaluate the variables as potential risk factors for lymph node metastasis. RESULTS: The incidence of T1 lesions was 8.6 percent. In the analysis cohort, the lymph node metastasis rate was 13 percent. Significant predictors of lymph node metastasis both univariately and multivariately were sm3 (P = 0.001), lymphovascular invasion (P = 0.005), and lesions in the lower third of the rectum (P = 0.007). Poorly differentiated carcinoma was significant univariately (P = 0.001) but not in the multivariate model. No other parameter was associated with a significant risk. CONCLUSIONS: T1 colorectal carcinomas with lymphovascular invasion, sm3 depth of invasion, and location in the lower third of the rectum have a high risk of lymph node metastasis. These lesions should have an oncologic resection. In a case of the lesion in the lower third of the rectum, local excision plus adjuvant chemoradiation may be an alternative.

Adenocarcinoma↗

PubMed2002

Muscle activation patterns in subjects with and without low back pain.

OBJECTIVE: To analyze muscle activation patterns during various footplate perturbations, used as proprioceptive challenges in patients with low back pain (LBP) and in controls. DESIGN: A prospective and controlled comparative study. SETTING: Outpatient clinic. PARTICIPANTS: Twenty subjects with chronic LBP and 20 age- and sex-matched controls. INTERVENTIONS: The subjects underwent 5 sets of footplate perturbations in 3 directions with 16 perturbations for each set. MAIN OUTCOME MEASURES: Latency, frequency, and asymmetry of muscle activation of the erector spinae, rectus abdominus, anterior tibialis, and gastrocnemius muscles were measured bilaterally with surface electromyography. RESULTS: In the toes-up movements, subjects with LBP were significantly less likely to activate their rectus abdominus muscles (P=.02), and they were more likely to exhibit asymmetric muscle activation in the smaller forward movements (odds ratio=4.1, P=.03). The latter result appears to be driven by asymmetric contraction of the erector spinae and rectus abdominus. CONCLUSIONS: Significantly more subjects with LBP than control subjects exhibited absent firing of trunk muscles during 2 of the 5 footplate perturbations. These results suggest an abnormality of the neuromuscular loop and may represent altered proprioception.

Adult↗

PubMedDate not supplied

A comparison of facial protection and the incidence of head, neck, and facial injuries in Junior A hockey players. A function of individual playing time.

A cohort of 282 elite amateur ice hockey players were analyzed to 1) record the number, type, location, and severity of head, neck, and facial injuries sustained during games; 2) examine the relationship between injuries and the type of facial protection (none, partial, or full) according to individual playing time; and 3) determine whether full or partial facial protection is associated with an increased incidence of concussions, eye injuries, and neck injuries. Fifty-two injuries (158.9 per 1000 player-game hours) occurred in players wearing no facial protection, 45 (73.5 per 1000 player-game hours) in players wearing partial facial protection (half shield), and 16 (23.2 per 1000 player-game hours) in players wearing full facial protection (full cage or shield). Players wearing no protection were injured at a rate more than twice that of players wearing partial protection and almost seven times higher than those wearing full protection. Concussions occurred in four players wearing no protection, five players wearing partial protection, and two players wearing full protection; these differences were not significant. The risk of eye injury was 4.7 times greater for players wearing no protection compared with those wearing partial protection. No eye or neck injuries occurred in players wearing full protection. This study demonstrates that both full and partial facial protection significantly reduce injuries to the eye and face without increasing neck injuries and concussions.

Athletic Injuries↗