Proposal of a 2-tier histologic grading system for canine cutaneous mast cell tumors to more accurately predict biological behavior.

Currently, prognostic and therapeutic determinations for canine cutaneous mast cell tumors (MCTs) are primarily based on histologic grade. However, the use of different grading systems by veterinary pathologists and institutional modifications make the prognostic value of histologic grading highly questionable. To evaluate the consistency of microscopic grading among veterinary pathologists and the prognostic significance of the Patnaik grading system, 95 cutaneous MCTs from 95 dogs were graded in a blinded study by 28 veterinary pathologists from 16 institutions. Concordance among veterinary pathologists was 75% for the diagnosis of grade 3 MCTs and less than 64% for the diagnosis of grade 1 and 2 MCTs. To improve concordance among pathologists and to provide better prognostic significance, a 2-tier histologic grading system was devised. The diagnosis of high-grade MCTs is based on the presence of any one of the following criteria: at least 7 mitotic figures in 10 high-power fields (hpf); at least 3 multinucleated (3 or more nuclei) cells in 10 hpf; at least 3 bizarre nuclei in 10 hpf; karyomegaly (ie, nuclear diameters of at least 10% of neoplastic cells vary by at least two-fold). Fields with the highest mitotic activity or with the highest degree of anisokaryosis were selected to assess the different parameters. According to the novel grading system, high-grade MCTs were significantly associated with shorter time to metastasis or new tumor development, and with shorter survival time. The median survival time was less than 4 months for high-grade MCTs but more than 2 years for low-grade MCTs.

The nine-banded armadillo (Dasypus novemcinctus) is an intermediate host for Sarcocystis neurona.

The nine-banded armadillo (Dasypus novemcinctus) is an intermediate host of at least three species of Sarcocystis, Sarcocystis dasypi, Sarcocystis diminuta, and an unidentified species; however, life cycles of these species have not been determined. Following feeding of armadillo muscles containing sarcocysts to the Virginia opossum (Didelphis virginiana), the opossums shed sporulated Sarcocystis sporocysts in their faeces. Mean dimensions for sporocysts were 11.0x7.5 microm and each contained four sporozoites and a residual body. Sporocysts were identified as Sarcocystis neurona using PCR and DNA sequencing. A 2-month-old foal that was negative for S. neurona antibodies in the CSF was orally inoculated with 5x10(5) sporocysts. At 4 weeks post-infection, the foal had a 'low positive' result by immunoblot for CSF antibodies to S. neurona and by week 6 had a 'strong positive' CSF result and developed an abnormal gait with proprioceptive deficits and ataxia in all four limbs. Based on the results of this study, the nine-banded armadillo is an intermediate host of S. neurona.

The striped skunk (Mephitis mephitis) is an intermediate host for Sarcocystis neurona.

Striped skunks, initially negative for antibodies to Sarcocystis neurona, formed sarcocysts in skeletal muscles after inoculation with S. neurona sporocysts collected from a naturally infected Virginia opossum (Didelphis virginiana). Skunks developed antibodies to S. neurona by immunoblot and muscles containing sarcocysts were fed to laboratory-reared opossums which then shed sporulated Sarcocystis sporocysts in their faeces. Mean dimensions for sporocysts were 11.0 x 7.5 microm and each contained four sporozoites and a residuum. Sarcocysts from skunks and sporocysts from opossums fed infected skunk muscle were identified as S. neurona using PCR and DNA sequence analysis. A 2-month-old, S. neurona-naive pony foal was orally inoculated with 5 x 10(5) sporocysts. Commercial immunoblot for antibodies to S. neurona performed using CSF collected from the inoculated pony was low positive at 4 weeks p.i., positive at 6 weeks p.i., and strong positive at 8 weeks p.i. Gamma-interferon gene knockout mice inoculated with skunk/opossum derived sporocysts developed serum antibodies to S. neurona and clinical neurologic disease. Merozoites of S. neurona present in the lung, cerebrum, and cerebellum of mice were detected by immunohistochemistry using polyclonal antibodies to S. neurona. Based on the results of this study, the striped skunk is an intermediate host of S. neurona.

The histopathologic diagnosis of subclinical Johne's disease in North American bison (Bison bison).

The morphologic changes of subclinical Johne's disease in North American Bison (Bison bison) are characterized by microgranulomas composed of epithelioid macrophages and individual multinucleate giant cells of Langhans'-type occasionally containing individual cytoplasmic acid-fast bacilli compatible with Mycobacterium avium paratuberculosis. The microgranulomas are best visualized in the mesenteric lymph nodes of infected subclinical animals. Macrophages that can be confused with infection-associated epithelioid macrophages in the mesenteric lymph nodes are pigment-carrying cells from the intestinal tract. Mesenteric lymph node biopsy may be a useful diagnostic tool for detection of mild subclinical infection in individual ruminants from herds of unknown infection status. The biopsy may also be useful for Johne's disease surveillance during test-and-cull programs.

Neurologic disease in gamma-interferon gene knockout mice caused by Sarcocystis neurona sporocysts collected from opossums fed armadillo muscle.

Fifteen gamma-interferon gene knockout mice were each orally inoculated with 5 x 10(3) Sarcocystis sporocysts derived from Virginia opossums (Didelphis virginiana) fed nine-banded armadillo (Dasypus novemcinctus) muscle containing sarcocysts. Three mice were inoculated with similarly obtained homogenates, but in which no sporocysts were detected. Mouse M8 was pregnant when inoculated and gave birth during the trial. Fifteen of 15 (100%) mice inoculated with sporocysts developed neurologic signs and/or died by day 30 d.p.i. One of 3 (33.3%) mice inoculated with homogenates in which no sporocysts were detected developed clinical signs and died at 34 d.p.i. All young of mouse M8 had maternally acquired antibodies to Sarcocystis neurona, but none developed clinical neurologic signs or had protozoal parasites in their tissues. All brains from mice that developed clinical signs contained merozoites that reacted positively to S. neurona antibodies using immunohistochemical techniques. Evidence from this study further supports the nine-banded armadillo being an intermediate host of S. neurona.

Evaluation of the shedding of Sarcocystis falcatula sporocysts in experimentally infected Virginia opossums (Didelphis virginiana).

Five Virginia opossums (Didelphis virginiana) were fed muscles of brown-headed cowbirds (Molothrus ater) containing sarcocysts of Sarcocystis falcatula. Shedding of sporocysts was confirmed in all five opossums by fecal flotation. Counts were conducted daily for 2 weeks and then biweekly until the animals were euthanized and necropsied. The average prepatent period was 9.8 (7-16) days. The number of sporocysts shed varied greatly between the opossums with maximum mean shedding occurring at 71.6 (26-112) days post-infection (DPI). Average sporocyst production was 1480 sporocysts/gram of feces (SPG). Maximum output was 37,000 SPG. Average fecal yield in captivity was 17.5g of feces/day. Opossums shed 25,900 sporocysts/day (average) and a maximum of 647,500 sporocysts/day. All opossums shed sporocysts until time of euthanasia (46-200 DPI). Histologically, numerous sporocysts were present in the lamina propria at necropsy, primarily in the proximal half of the small intestine. Sporocysts were generally in clusters within the lamina propria of the luminal two-thirds of the villi. Sporocysts were found less frequently in the epithelium. No evidence of ongoing gametogony or other development was evident.

Immunoconversion against Sarcocystis neurona in normal and dexamethasone-treated horses challenged with S. neurona sporocysts.

Equine protozoal myeloencephalitis is a common neurologic disease of horses in the Americas usually caused by Sarcocystis neurona. To date, the disease has not been induced in horses using characterized sporocysts from Didelphis virginiana, the definitive host. S. neurona sporocysts from 15 naturally infected opossums were fed to horses seronegative for antibodies against S. neurona. Eight horses were given 5x10(5) sporocysts daily for 7 days. Horses were examined for abnormal clinical signs, and blood and cerebrospinal fluid were harvested at intervals for 90 days after the first day of challenge and analyzed both qualitatively (western blot) and quantitatively (anti-17kDa) for anti-S. neurona IgG. Four of the challenged horses were given dexamethasone (0.1mg/kg orally once daily) for the duration of the experiment. All challenged horses immunoconverted against S. neurona in blood within 32 days of challenge and in CSF within 61 days. There was a trend (P = 0.057) for horses given dexamethasone to immunoconvert earlier than horses that were not immunosuppressed. Anti-17kDa was detected in the CSF of all challenged horses by day 61. This response was statistically greater at day 32 in horses given dexamethasone. Control horses remained seronegative throughout the period in which all challenged horses converted. One control horse immunoconverted in blood at day 75 and in CSF at day 89. Signs of neurologic disease were mild to equivocal in challenged horses. Horses given dexamethasone had more severe signs of limb weakness than did horses not given dexamethasone; however, we could not determine whether these signs were due to spinal cord disease or to effects of systemic illness. At necropsy, mild-moderate multifocal gliosis and neurophagia were found histologically in the spinal cords of 7/8 challenged horses. No organisms were seen either in routinely processed sections or by immunohistochemistry. Although neurologic disease comparable to naturally occurring equine protozoal myeloencephalitis (EPM) was not produced, we had clear evidence of an immune response to challenge both systemically and in the CNS. Broad immunosuppression with dexamethasone did not increase the severity of histologic changes in the CNS of challenged horses. Future work must focus on defining the factors that govern progression of inapparent S. neurona infection to EPM.

Viability of Sarcocystis neurona sporocysts and dose titration in gamma-interferon knockout mice.

Gamma-interferon knockout mice have become the model animal used for studies on Sarcocystis neurona. In order to determine the viability of S. neurona sporocysts and to evaluate the course of the disease in these mice, sporocysts were collected from opossums (Didelphis virginiana), processed, and stored for varying periods of time. Gamma-interferon knockout mice were then inoculated orally with different isolates at different doses. These animals were observed daily for clinical signs until they died or it appeared necessary to humanely euthanize them. 15 of 17 (88%) mice died or showed clinical signs consistent with neurologic disease. The clinical neurologic symptoms observed in these mice appeared to be similar to those observed in horses. 15 of 17 (88%) mice were euthanized or dead by day 35 and organisms were observed in the brains of 13 of 17 (77%) mice. Dose appeared not to effect clinical signs, but did effect the amount of time in which the course of disease was completed with some isolates. The minimum effective dose in this study was 500 orally inoculated sporocysts. Efforts to titrate to smaller doses were not attempted. Direct correlation can be made between molecularly characterized S. neurona sporocysts and their ability to cause neurologic disease in gamma-interferon knockout mice.

Influence of size of sporocyst inoculum upon the size and number of sarcocysts of Sarcocystis falcatula which develop in the brown-headed cowbird.

The influence of the number of sporocysts in the inoculum of Sarcocystis falcatula on the morphology of the sarcocysts has not been reported in the literature. To determine if there is a relationship, different number of sporocysts were inoculated orally into wild-caught cowbirds. After 14 weeks, the cowbirds were euthanised and muscle tissue was examined grossly and by histologic sections. Sarcocysts were compared based on the numbers which developed and their sizes. There was a linear increase in the number of sarcocysts as the size of the inoculum increased, however, the size of the sarcocysts became smaller with the increase in number of sporocysts inoculated.

Are Sarcocystis neurona and Sarcocystis falcatula synonymous? A horse infection challenge.

Equine protozoal myeloencephalitis (EPM) is a debilitating neurologic disease of the horse. The causative agent. Sarcocystis neurona, has been suggested to be synonymous with Sarcocystis falcatula, implying a role for birds as intermediate hosts. To test this hypothesis, opossums (Didelphis virginiana) were fed muscles containing S. falcatula sarcocysts from naturally infected brown-headed cowbirds (Molothrus ater). Ten horses were tested extensively to ensure no previous exposure to S. neurona and were quarantined for 14 days, and then 5 of the horses were each administered 10(6) S. falcatula sporocysts collected from laboratory opossums. Over a 12-wk period, 4 challenged horses remained clinically normal and all tests for S. neurona antibody and DNA in serum and cerebrospinal fluid were negative. Rechallenge of the 4 seronegative horses had identical results. Although 1 horse developed EPM, presence of S. neurona antibody prior to challenge strongly indicated that infection occurred before sporocyst administration. Viability of sporocysts was confirmed by observing excystation in equine bile in vitro and by successful infection of naive brown-headed cowbirds. These data suggest that S. falcatula and S. neurona are not synonymous. One defining distinction is the apparent inability of S. falcatula to infect horses, in contrast to S. neurona, which was named when cultured from equine spinal cord.

Primary malignant histiocytosis of the brain in a dog.

Malignant histiocytosis is a well-recognized canine tumour, occurring primarily in Bernese mountain dogs and characterized by disseminated histiocytic infiltration of multiple visceral organs. This report describes the light microscopical and ultrastructural features of a neoplasm composed of malignant histiocytes and confined to the brain. A poorly demarcated mass in the right parieto-occipital lobe of a miniature schnauzer was composed of loosely aggregated, pleomorphic cells with abundant eosinophilic cytoplasm, expanding the meninges. Many binucleated and multinucleated giant cells and mitotic figures were seen. Immunohistochemically, the tumour cells reacted intensely for lysozyme. Ultrastructurally, the neoplastic cells had features of histiocytic cells with abundant lysosomes. The findings in this case were strikingly similar to those of disseminated malignant histiocytosis described in other dog breeds.

Clinical, urodynamic, and histologic effects of urethral intussusception in clinically normal dogs.

OBJECTIVE: To evaluate clinical and histologic effects of surgically created urethral intussusception and determine whether it creates a high-pressure zone that resists passive urine flow in clinically normal dogs. ANIMALS: 8 healthy adult sexually intact female dogs. PROCEDURE: Urethral pressure profilometry was used to measure maximal urethral closure pressure (MUCP) and functional profile length (FPL) in dogs sedated with xylazine hydrochloride and atropine before and 2, 4, 7, 14, 28, 60, and 90 days after surgery. Cystourethral leak point pressure (CLPP) and cystourethral leak point volume (CLPV) were determined in anesthetized dogs immediately before and after surgery. Dogs were assigned to 4 groups of 2 dogs each; groups were euthanatized 4, 14, 28, and 90 days later, and representative tissues were examined. RESULTS: Dog 1 developed complete postoperative urethral obstruction. The procedure was altered, and all dogs recovered without complication. Mild inflammation attributable to surgical manipulation, but not ischemic damage or reduction of the intussusception, was evident. Comparison of preoperative MUCP and FPL with postoperative values did not yield significant differences. Immediate postoperative CLPP and CLPV were significantly higher than preoperative values, but were not significantly increased at euthanasia. A distinct but nonsignificant pressure spike was observed in postoperative urethral pressure profiles and persisted in 7 of 8 dogs. CONCLUSIONS: Urethral intussusception does not have deleterious effects when performed as described. Urodynamic data do not support the premise that urethral intussusception will create a high-pressure zone in the urethra that will resist passive urine flow long term in clinically normal dogs.

Effects of three sedative protocols on glomerular filtration rate in clinically normal dogs.

OBJECTIVE: To determine the effects of 3 sedative protocols (butorphanol and diazepam [BD] IV; acepromazine and butorphanol [AB] IV; diazepam and ketamine [DK] IV) on glomerular filtration rate (GFR) as measured by 99mTc DTPA nuclear scintigraphy and to compare them with GFR measured without sedation. Cardiovascular, respiratory, and sedative effects of each protocol also were measured. ANIMALS: 12 adult male Walker Hounds. PROCEDURE: Systolic, diastolic, and mean arterial blood pressures and heart and respiratory rates were measured before, during, and after scintigraphic measurement of GFR. RESULTS: Difference in GFR was not significant between any of the sedative regimens and the control. The DK protocol caused significant increases in systolic, diastolic, and mean arterial blood pressure; compared with the AB and BD protocols, it caused significant increases in heart rate versus all protocols, and was associated with the lowest mean GFR (2.80 ml/min/kg of body weight). The AB protocol caused significant decreases in systolic, diastolic, and mean arterial blood pressures, compared with DK and the nonsedation protocols. Mean GFR for the BD protocol was 2.94 ml/min/kg, and was 3.13 ml/min/kg for the AB and the nonsedation protocols. The AB protocol provided the best sedation with minimal additional restraint required. The BD and nonsedation protocols often were associated with substantial dog movement. The DK protocol induced inadequate duration of immobilization (< 10 minutes) in some dogs and excitement in others. CONCLUSION: GFR measurements obtained with any of the sedative protocols were not significantly different, compared with measurements in awake dogs. The AB protocol provides the best sedative effects and was associated with GFR values identical to those in awake dogs. Systemic hypotension caused by acepromazine did not decrease GFR in clinically normal dogs.

Gastric hemorrhage in dogs given high doses of methylprednisolone sodium succinate.

OBJECTIVE: To determine whether healthy dogs given high doses of methylprednisolone sodium succinate (MPSS) develop gastrointestinal tract ulcers and hemorrhage. ANIMALS: 19 healthy male hound-type dogs. PROCEDURE: Dogs were assigned randomly to intravenously receive high doses of MPSS (30 mg/kg of body weight, initially, then 15 mg/kg 2 and 6 hours later, and, subsequently, every 6 hours for a total of 48 hours; n = 10) or an equal volume of saline (0.9% NaCl) solution (9). Gastroduodenoscopy was performed before and after treatment. Endoscopic evidence of gross hemorrhage in the cardia, fundus, antrum, and duodenum of each dog was graded from none (0) to severe (3), and a total stomach score was calculated as the sum of the regional gastric scores. Number of ulcers were recorded. The pH of gastric fluid and evidence of occult gastric and fecal blood were measured. Food retention was recorded. RESULTS: Gastric hemorrhage was evident in all dogs after MPSS administration and was severe in 9 of 10 dogs but not visible in any dog after saline treatment. Occult gastric blood was detected more commonly (9/10 vs 2/9), median gastric acidity was greater (pH 1 vs pH 3), and food was retained more commonly (7/10 vs 1/9) in the stomach of MPSS-treated dogs. CONCLUSIONS AND CLINICAL RELEVANCE: High doses of MPSS cause gastric hemorrhage in dogs. All dogs treated with high doses of MPSS should be treated with mucosal protectants or antacids to prevent gastric hemorrhage.

Efficacy of misoprostol in prevention of gastric hemorrhage in dogs treated with high doses of methylprednisolone sodium succinate.

OBJECTIVE: To determine whether administration of misoprostol prevents gastric hemorrhage in healthy dogs treated with high doses of methylprednisolone sodium succinate (MPSS). ANIMALS: 18 healthy hound-type dogs of both sexes. PROCEDURE: All dogs were given high doses of MPSS (30 mg/kg of body weight, initially, then 15 mg/kg 2 and 6 hours later, and, subsequently, q 6 h for a total of 48 hours) IV. Dogs were assigned randomly to receive concurrent treatment with misoprostol (4 to 6 microg/kg, PO, q 8 h; n = 9) or an empty gelatin capsule (9). Gastroduodenoscopy was performed before and after treatment. Hemorrhage was graded from none (0) to severe (3) for each cardia, fundus, antrum, and duodenum. A total stomach score was calculated as the sum of the regional stomach scores. Food retention was recorded, and pH of gastric fluid was determined. Gastric and fecal occult blood was measured. RESULTS: Gastric hemorrhage was evident in all dogs after MPSS administration, and its severity was similar in both groups. Median total stomach score was 6 for misoprostol-treated dogs and 5.5 for dogs given the gelatin capsule. Difference in gastric acidity, frequency of food retention, and incidence of occult blood in gastric fluid and feces was not apparent between the 2 groups. CONCLUSIONS AND CLINICAL RELEVANCE: Administration of misoprostol (4 to 6 microg/kg, PO, q 8 h) does not prevent gastric hemorrhage caused by high doses of MPSS. Alternative prophylactic treatment should be considered.

Scintigraphic, sonographic, and histologic evaluation of renal autotransplantation in cats.

OBJECTIVE: To determine scintigraphic, sonographic, and histologic changes associated with renal autotransplantation in cats. ANIMALS: 7 adult specific-pathogen-free cats: 5 males, 2 females, 1 to 9 years old. PROCEDURE: Renal autotransplantation was performed by moving a kidney (5 left, 2 right) to the left iliac fossa. Before and at multiple times after surgery, for a total of 28 days, cats were evaluated by B-mode and Doppler ultrasonography, scintigraphy, and renal biopsy. RESULTS: By 24 hours after surgery, a significant decrease (42%) in mean glomerular filtration rate (GFR) and an increase in mean renal size (81% increase in cross-sectional area) were evident in the transplanted kidney, compared with preoperative values. By postsurgery day 28, reduction in GFR was 23%. Significant changes in renal blood flow velocity were identified in both kidneys. Consistent changes in resistive index or pulsatility index for either kidney could not be identified. When all postoperative histologic data were combined, the histologic score, indicating degree and numbers of abnormalities detected, for the transplanted kidney was significantly higher than that for the control kidney. CONCLUSIONS: Significant changes in renal function, size, and histologic abnormalities develop secondary to acute tubular necrosis in cats after uncomplicated renal autotransplantation. CLINICAL RELEVANCE: Evaluation of renal size and function may be of benefit for clinical evaluation of feline renal transplant patients, whereas measurement of the resistive index may be of little clinical value.

Removal of a thymoma via median sternotomy in a rabbit with recurrent appendicular neurofibrosarcoma.

A 9-year-old rabbit was evaluated for a mass on the right elbow. As a result of preoperative radiography, another mass was identified in the cranial portion of the mediastinum. Ultrasound guided fine needle aspiration was used for cytologic evaluation of the mass in the mediastinum and resulted in a presumptive diagnosis of thymoma. A median sternotomy approach was chosen to allow wide exposure for meticulous dissection in the cranial portion of the thoracic region. Histologic examination and immunoperoxidase labeling of lymphocytes with CD3 (a T cell marker) confirmed the diagnosis. The mass on the right elbow was subsequently removed and identified as a neurofibrosarcoma. Multiple appendicular masses that developed at separate locations and distinct times were excised and classified as locally invasive primary neurofibrosarcomas. Postmortem examination 9 months after initial evaluation confirmed recurrence of the neurofibrosarcoma at previous surgical sites. Gross or histologic evidence of thymoma was not evident. Prognosis is dismal for incompletely excised soft tissue sarcomas, because they are locally invasive and often recur.

Regression of subcutaneous lymphoma following removal of an ovarian granulosatheca cell tumor in a horse.

A 9-year-old Arabian mare was admitted for evaluation of multiple subcutaneous nodules and infertility. Fine-needle aspiration of one of the subcutaneous nodules resulted in a cytologic diagnosis of histiolymphocytic lymphoma. Palpation per rectum and transrectal ultrasonography revealed a mass associated with the left ovary. Excision of the ovarian tumor was performed, and a histopathologic diagnosis of granulosa-theca cell tumor was made. After removal of the granulosa-theca cell tumor, subcutaneous nodules regressed. The referring veterinarian reported that the nodules had also disappeared and then recurred after administration of a synthetic progestin. To further characterize the lymphoma and investigate this possible hormonal relationship, immunophenotyping and estrogen and progesterone receptor assays were performed. The subcutaneous lymphoma was classified as a T-cell rich B-cell lymphoma, results of estrogen receptor assays were negative, and results of progesterone receptor assays were positive. Clinical observations of subcutaneous lymphoma in horses indicate that the waxing and waning nature of these tumors may be associated with the estrous cycle, pregnancy, foaling, and lactation. Clinical observations and identification of progesterone receptors suggest that a relationship between serum steroid hormone concentrations, such as estrogen and progesterone, and subcutaneous lymphoma may exists.

Septic cholangiohepatitis and cholangiocarcinoma in a horse.

Septic cholangiohepatitis was diagnosed in an 11-year-old Warmblood gelding with a history of intermittent colic and fever. Klebsiella pneumoniae, susceptible to gentamicin, was cultured from the biopsy specimen. However, treatment with gentamicin was unsuccessful, and histologic examination and bacteriologic culture of a biopsy specimen obtained 3 weeks later revealed progression of the hepatic inflammation and yielded growth of gentamicin-resistant K pneumoniae. At this time, several discrete hyperechoic structures, suggestive of biliary calculi, were seen ultrasonographically. A change in antibiotic treatment was associated with gradual resolution of clinical signs. Five months after initial examination, the horse had a sudden onset of severe right forelimb lameness. The horse responded to treatment with antibiotics and phenylbutazone, but lameness and fever that was unresponsive to treatment recurred 7 months later, and the horse was euthanatized. Necropsy revealed nodules throughout the liver and a mass associated with the right metacarpophalangeal joint. Histologic and immunohistochemical examination revealed carcinomatous infiltration of the liver and metacarpophalangeal joint. The tumor was probably of biliary origin. Carcinoma should be considered in cases of septic cholangiohepatitis unresponsive to antibiotic treatment.

Adult-onset motor neuron disease in three cats.

Motor neuron diseases of domestic animals have rarely been described. Three cats with adult-onset, chronic, progressive generalized muscle weakness characterized initially by trembling on exertion and later by extreme difficulty in walking, cervical ventroflexion, dysphagia, and marked muscle atrophy were elevated. Spinal reflexes were evident early but were nondetectable as the disease progressed. Electromyography revealed fibrillation potentials, with nerve conduction velocities within the reference range. Histologic examination of muscle specimens revealed denervation. Marked neuron loss and gliosis were detected in the ventral horns of the spinal cord, with atrophy of ventral nerve rootlets. Less dramatic neuron loss was seen in brain stem motor nuclei. Electron microscopic examination of the ventral horns disclosed hypertrophied astrocytes, with densely arrayed intermediate filaments, swollen axons with large filamentous accumulations, and many macrophages with lipofuscin-like inclusions. Clinical and pathologic findings were consistent with a progressive neurodegenerative disease affecting spinal and some bulbar motor nuclei.