[Tuberculosis cutis luposa gigantea with Mycobacterium bovis detection]

In an 80-year-old woman, retired farmworker, we observed lupus vulgaris extending over more than half of her leg. The extreme size of the affected area made us talk of a giant form in this case. Bacteriological investigation revealed Mycobacterium bovis. The minimal amount of tuberculin required to induce a positive intradermal reaction was 10 IU (GT Behring). Another case with similar dimensions (reported by Christiansen in 1967) had been caused by Mycobacterium avium and developed over a period of at least 5 years. The vast cutaneous affection of our patient, in contrast, had developed within only one year, starting from a brownish macula of the size of a palm on her upper leg. This macula - presumably the manifestation of quiescent lupus vulgaris - had not changed for more than 40 years. This late exacerbation of post-primary tuberculosis might have been favored by the patient's reduced immunologic resistance on account of her advanced age. In addition, local cofactors - namely ankylosis of her knee and contact eczematous dermatitis - have to be considered. In accordance with the resistogram, the disease responded to monotherapy with isoniazide.

Structure, cellular distribution, and functional characteristics of the guinea pig leucocyte common antigen

The guinea pig leucocyte common antigen (LCA), expressed on different hemopoietic cells, was examined using the monoclonal antibody (mAb) H 201. Immunohistology and FACS analysis revealed that T and B lymphocytes, macrophages, and thymocytes express the H 201 epitope in comparable density. The level of LCA-expression increased during the course of maturation and activation of T cells. Differences in the molecular weight of LCA were observed, which depended on the nature of various cell populations, indicating that in each case alternative variants of LCA are expressed. The molecular weight of guinea pig LCA ranged from 175 kDa on thymocytes, up to a 230-kDa variant found on B lymphocytes. Antigen- or alloantigen-induced T cell activation in vitro was moderately affected by the continuous presence of mAb 201. In contrast, the PHA-mediated T cell proliferation was strongly and selectively enhanced, supporting the assumption of an LCA involvement in the "alternative pathway" of T cell activation.

[Systemic photochemotherapy (PUVA) in acanthosis nigricans maligna: regression of keratosis, hyperpigmentation and pruritus]

We report on a 60-year-old patient, who developed malignant acanthosis nigricans (MAN) with intense itching 2 years after a large-cell bronchial carcinoma had been diagnosed and found inoperable. The MAN became manifest at a phase of full clinical remission of the lung tumor, which had been treated with cytostasis (cisplatin, vindesine), high energy irradiation, and extirpation of the lymph node metastases. One year after onset of MAN, the lung tumor relapsed, accompanied by an elevated serum level of carcinoembryonic antigen (CEA). The patient was slightly obese, but not diabetic. The generalized MAN was treated with 18 exposures to systemic PUVA (photochemotherapy) over 9 weeks. The patient received 8-methoxypsoralene (8-MOP) orally and a total UVA dose of 52 J/cm2; the last exposure amounted to a maximum dose of 4 J/cm2. Under this treatment, the patient was completely relieved from tormenting pruritus; in addition, we observed significant regression of the pigmented keratoses as well as the intertriginous maceration.

Influence of sulfated carbohydrates on the accessibility of CD4 and other CD molecules on the cell surface and implications for human immunodeficiency virus infection

The modulatory activity of dextran sulfate with a relative molecular mass of 8 and 500 kDa and pentosan polysulfate with a relative molecular mass of 6 kDa on human T cell surface molecules CD2, CD3, CD4, CD8 and HLA-DR was investigated by analytical flow cytometry. The 500-kDa dextran sulfate induces a complete disappearance of the CD4 and a 50% diminution of CD2 immune reactivity on peripheral blood lymphocytes after a 4-h incubation while the low molecular mass polyanions do not. This modulation of the CD4 immune reactivity includes all CD4 epitopes investigated. It does not correlate with the antiviral effect of polyanions against human immunodeficiency virus infection. The interaction of polyanions with the CD4 presentation is temperature dependent and differs between fresh lymphocytes and immortal cell lines. From our data it can be concluded that mechanisms other than cell surface effects are responsible for the antiviral potency of these drugs. Implications for the modes of antiviral action of sulfated carbohydrates are discussed.

[Hypereosinophilia syndrome--successful PUVA therapy]

A 71-year-old female patient with monosymptomatic hypereosinophilic syndrome is presented. Other dermatological and internal diseases associated with eosinophilia were excluded. The patient had an excellent response to photochemotherapy (PUVA).

Epidermal cell growth-dependent arylhydrocarbon-hydroxylase (AHH) activity in vitro

Cytochrome P-450-dependent arylhydrocarbon-hydroxylase (AHH) activity and inducibility by benzanthracene (BA) was measured in cultured guinea pig and human epidermal cells. Basal AHH-activity (AHHb) in guinea pig epidermal cells was much higher than in human epidermal cells. AHHb in guinea pig epidermal cells was directly related to the labeling index and decreased to the original level between the 5th and 7th day of cell culturing. On the other hand, the induction-ratio of AHH reached its maximum level when the number of cells began to rise (proliferation phase) and remained high at day 7 of the cell culture. These results suggest a cell growth dependent activity and inducibility of carcinogen-metabolizing enzymes, such as AHH, in isolated epidermal cells.

[Repigmentation treatment of vitiligo with L-phenylalanine and UVA irradiation]

20 patients suffering from vitiligo (17 with generalized, 3 with localized type) were treated with L-phenylalanine and UV-A irradiation (PAUVA). The dose of L-phenylalanine was 50 mg/kg per os. In 85% of the patients, this therapy resulted in a follicular and partially confluent repigmentation, which did not exceed 50% of the vitiliginous area.

[Urticaria vasculitis and sulfone, a case report]

Systemic corticosteroids play a predominant role in the treatment of urticarial vasculitis (U.V.). If steroids are contraindicated, there may be applied a variety of pharmacologically different compounds. A female patient suffering from U.V. and metabolic syndrome, who had not shown any positive response to indomethacin, H1 and H2 antagonists, or colchicine, was treated with dapsone. As a result, the clinical symptoms improved within a few days and her hypocomplementemia normalized. We discuss the possible mechanisms of action of sulphones in U.V.

Retinoids in cutaneous T cell lymphomas

Sixteen patients - 12 with cutaneous T cell lymphoma (CTCL), 1 with Sézary syndrome, 1 with actinic reticuloid, and 2 with parapsoriasis variegata - were treated with either a new, potent arotinoid alone or with combined etretinate (Tigason) and PUVA therapy (Re-PUVA). 92% of all patients showed a minor up to a distinct response of their skin lesions within 12.6 +/- 7.4 weeks. More than 50% of the skin lesions cleared in 67% of the patients. After discontinuation of the retinoid therapy, relapses occurred in all cases within 3-10 weeks. There was no difference between the therapeutic efficacy of arotinoid alone and the Re-PUVA regimen, but the latter was less toxic.

[In vitro model of the re-epithelialization of defects]

Epidermal cells taken from guinea pigs were cultured on collagen in order to study the processes comparable to reepithelialization of wounds by means of time-lapse cinematography and electron microscopy. Attachment and spreading of the cells are essential for the following cell proliferation. Immediately after seeding, the cells move in streams and rotate around their axes. Flattened cells show cytoplasmic streaming and ameboid movement as they continuously alter their shapes (10-25 microns/h). The cells actively form intercellular bridges, which favor the confluence of the cells. In the present study, the phases of attachment, intercellular association, and formation of colonies have been classified and related to the activity of the DNA synthesis, as it was indicated by 3H-thymidine incorporation.

[Epidermal cell cultures--significance for wound coverage in the human]

Epithelial sheets can be cultivated from isolated epidermal cells; in this way, it is possible to increase the cell number considerably. H. Green and co-workers were the first to make use of such epithelia for the autologous covering of burn wounds. We modified this method and report on our experiences with this technique in a patient with small skin defects.

[Treatment of hydrofluoric acid burns]

A chemical-plant worker sustained hydrofluoric acid burns during cleaning procedures. Intra-arterial perfusion and intralesional injections of calcium gluconate solution prevented progression of the burns into deeper tissue layers.

Analysis of chromatin changes associated with the expression of globin and non-globin genes in cell hybrids between erythroid and other cells

Red blood cell differentiation involves the coordinate expression of a set of polypeptides some of which are erythroid-specific (the abundant globins as well as minor species such as glycophorin, carbonic anhydrase I and the RBC lipoxygenase) whereas others are found also in a subset of other cells, e.g. beta spectrin and a 19 kd polypeptide (ep 19) found in adult liver and kidney as well as erythroid cells. To investigate the genetic mechanisms involved in the regulation of these classes of genes, the expression of lipoxygenase, ep 19 and beta globin mRNAs was investigated in cell hybrids between mouse erythroid (Friend) cells and mouse T-lymphoma or neuroblastoma cells. All three mRNAs are expressed or repressed together in cell hybrids between the Friend cell and lymphoma or neuroblastoma cells respectively. Moreover, studies of the chromatin structure surrounding the genes reveal that erythroid cell-specific DNaseI hypersensitive sites within the ep 19 and beta major globin genes are lost in the Friend cell X neuroblastoma hybrids whereas they are retained in the Friend cell X lymphoma cell hybrids. This implies that the trans-acting mechanism responsible for regulating the RBC phenotype in these cell hybrids acts at the level of the early chromatin changes thought to reflect a pre-activation stage in gene expression.

[Simultaneous occurrence of metageria and Gottron's acrogeria in one family]

We report on a 17-year-old patient suffering from generalized mottled hyperpigmentation and multiple telangiectatic lesions of the skin. The subcutaneous fatty tissue was lacking or deficient. The patient showed a bird-like face. The cutaneous changes had been present since birth. X-ray studies revealed acro-osteolysis of the hands and feet. The metabolic and endocrine data were within normal ranges except of latent hypothyroidism. The clinical picture presented all criteria of metageria. The patient's mother and sister showed similar cutaneous changes, however, restricted to the distal parts of the extremities. We diagnosed acrogeria Gottron. The incidence of both metageria and acrogeria in one family makes metageria as an independent entity doubtful.

[Generalized verrucosis in familial T-helper cell deficiency. Treatment with interferon and Tigason]

We report on a 17-year-old patient suffering from generalized verrucosis. This diagnose had been confirmed by means of light microscopy, electron microscopy, and DNA hybridisation (HPV type 2). The study of immunological parameters revealed reduced numbers of T-lymphocytes, especially of helper-T-cells. Skin tests with recall antigens were normal. Three brothers of our patient showed slight reduction of helper-T-cells. Treatment with topical retinoic acid was not effective. Treatment with alpha-interferon i.m. intralesionally was effective in the beginning, but two weeks after onset of therapy no further improvement could be achieved. Discontinuation of therapy was followed by a relapse. Tigason which was given thereafter led to flattening of the warts but failed to bring about complete regression within the following four months.

[Treatment of mycosis fungoides with Zovirax (acyclovir). Study of 2 patients]

We report on two female patients suffering from mycosis fungoides, tumorous type but without systemic involvement, who have been treated with 400 mg Zovirax (Acyclovir) 3 times daily (about 15 mg/kg/day) for 12 days. The follow-up period amounted to 11 and 14 days, respectively. This therapy did not result in regression of the disease; one patient even showed progression of her skin tumors.

[Preliminary results of Re-PUVA therapy in cutaneous T-cell lymphomas]

Eight patients with T-cell-lymphoma of the skin (6 mycosis fungoides, 2 parapsoriasis variegata) were treated with Tigason in combination with PUVA-therapy. The daily dose of Tigason was 50-100 mg. There was complete regression of skin lesions in three patients, partial regression in three patients, and an improvement in two patients.

[Motor unit potentials of the biceps muscle in comparing right and left parameters in right-handed subjects]

Motor unit potentials recorded by a concentric needle electrode in the right and left m. biceps brachii were statistically compared with regards to mean potential duration and amplitude. With the Wilcoxon-test the mean duration showed no statistically significant right/left difference, whereas the mean potential amplitude turned out to be significantly higher in the left m. biceps (Fig. 1, 2, table 1). The fibre density measured by a single fibre EMG electrode was found to be higher in the left m. biceps as well (1.23 as compared to 1.18 in the right). Therefore it is assumed that muscle fibre hypertrophy in muscles of the right arm in right-handed subjects leads to a decrease in fibre density within the motor units. The mean distance between active muscle fibres and electrode seems to be a more important factor with regards to the unit potential's amplitude than the muscle fibre diameter itself.

[Acyclovir in mycosis fungoides]

Acyclovir was not effective in the treatment of two patients with a tumor-stage mycosis fungoides.

[Classical form of Kaposi sarcoma: immunology and interferon therapy]

T-lymphocytes and their subsets were determined in three patients with classical Kaposi's sarcoma. A reduction of pan-T-lymphocytes, including both a reduction of T-helper and T-suppressor cells, was found in one patient. None of the patients showed a reduction of the T-helper/T-suppressor cell ratio, as described in the lymphadenopathic disseminated type of Kaposi's sarcoma. Intradermal testing with tuberculin and trichophytin gave no indication of humoral immunodeficiency or anergy. In addition to electron beam irradiation, one female patient was treated with rIFN-alpha-interferon, 6 X 10(6) IU 3 times a week over a period of 3 months, and 18 X 10(6) IU 3 times weekly over 1 month. Under this therapy, irradiated as well as nonirradiated lesions become flatter, reduced in size and faded. The number of T-suppressor cells diminished.

[Areas of low-threshold motor units in the m. extensor digitorum communis--study using concentric needle electrodes]

By a slight voluntary contraction, recording sites were chosen where the electrode picked up activity of only one motor unit. Then the needle was moved in minute steps (as controlled by a slide-gauge) through the area of the motor unit under investigation. Hereby the recorded motor unit potential underwent characteristic changes (Fig. 1). The amplitude was maximal within the centre of the motor unit and decreased sharply within 1 to 2 mm (Fig. 2, 3). Single spike components, when discernible within the motor unit potential complex, could be traced for about 1 mm. With regards to the amplitude profile curves of the whole motor unit potential, it is discussed whether a population of fairly small low-threshold motor units exists in the EDC containing as few as 20-50 muscle fibres scattered over an area with a diameter of 1-2 mm.

Human atherosclerosis. I. Cell constitution and characteristics of advanced lesions of the superficial femoral artery

This study represents a systematic analysis of the fine-structural characteristics of atherosclerotic lesions of the superficial femoral artery in man together with the growth characteristics in culture of the smooth muscle cells derived from these lesions. Occlusive fibrous atherosclerotic plaques were obtained from 29 male patients at the time of bypass surgery for occlusion of the superficial femoral artery and were studied by light and transmission electron microscopy. The occluded segment of each artery was obtained immediately after removal from the patient and examined with sterile techniques, and representative segments were fixed for light- and electron-microscopic study. Adjacent segments were used for dissection of the lesion away from the underlying media, and smooth muscle cells were cultured from lesion and nonlesion areas and compared in terms of their growth responses to increasing concentrations of a pool of human whole blood serum. The majority of the lesions were fibroproliferative and contained relatively little lipid. The fibrous cap that covered each lesion consisted of a special form of dense connective tissue that contained flat, pancake-shaped smooth muscle cells in a lacunalike space. This space consisted of concentric layers of basement membrane, collagen fibrils, and proteoglycan. The majority of the cells beneath the fibrous cap were smooth muscle cells mixed with small but varying numbers of macrophages. Most of the lesions were occluded by a thrombus, which had undergone organization and recanalization. A small number of the lesions had deep lipid deposits together with foci of degeneration and calcification. The occluded thrombi contained smooth muscle cells and a larger proportion of macrophages than the lesions themselves. The in vitro growth properties of the smooth muscle cells isolated from the lesion and the underlying media suggested that the lesion cells had senesced, compared with the medial smooth muscle cells derived from the same artery.

[Chemotherapy of cutaneous T-cell lymphomas with arotinoid]

Five patients with T-cell lymphoma of the skin (mycosis fungoides; Sézary syndrome) were given parenterally arotinoid ethyl ester (Ro 13-6298) at a daily dose of 0.5-4.0 micrograms/kg body weight, to a total dose of 20 mg over maximally 31 weeks. In three patients, among them one with tumourous mycosis fungoides, there was complete regression of the cutaneous lesions. In another patient the cutaneous changes, some of them with ulceration, regressed so that there were only residual infiltrates. In the case of the Sézary syndrome there was no response. Most important side-effects of treatment were cheilitis, moist and sticky skin, paronychia and dry mucosae. The most serious side-effect was pain in muscles, joints and bones. There were no significant changes in biochemical values during the treatment.

Intranuclear tonofilament-like filaments in skin carcinoma

Electron microscopical investigations of untreated solar keratosis, squamous cell carcinoma, and Bowen carcinoma showed intranuclear bundles of intermediate filaments in suprabasal keratinocytes. We found evidence that the filaments are incorporated into the nucleus during atypical mitosis.

[Multilocular progressive lipoatrophia semicircularis]

Report on a 51-year-old adipose patient suffering from a rapidly progressing lipatrophia semicircularis. The lipoatrophy occurred in the form of numerous lesions on the trunk and limbs.

[Cheilitis glandularis simplex]

Cheilitis glandularis simplex is a rather rare disease which has to be differentiated from cheilitis granulomatosa. The histological characteristics of cheilitis glandularis simplex are hypertrophy and hyperplasia of mucous and/or heterotopic salivary glands. The therapy is the excision of the tumor.

Temporary intraluminal shunts: resolution of a management dilemma in complex vascular injuries

Complex vascular injuries of the extremities in which acute arterial insufficiency is combined with severe or prolonged shock, extended periods of ischemia, or associated fractures or soft-tissue injuries have unacceptably high limb loss rates, frequently because the allowable warm ischemia time for skeletal muscle is exceeded before adequate revascularization. In a 1-year period, ten patients with complex vascular injuries identified at our metropolitan trauma center underwent routine introduction of temporary plastic intravascular shunts at the site of vessel disruption, thus permitting immediate limb revascularization. This rapid reperfusion permitted appropriate attention to be directed toward skeletal fixation, soft-tissue debridement, and other procedures without the urgency usually associated with the presence of acute limb ischemia. Following various local and distant orthopedic or general surgical procedures, arterial and venous continuity were uneventfully re-established. This experience suggests that the routine use of plastic intraluminal shunts in complex vascular injuries of the extremities has the distinct potential of reducing the excess morbidity from prolonged acute arterial insufficiency noted in such injuries.

Indium-111 platelet imaging for detection of platelet deposition in abdominal aneurysms and prosthetic arterial grafts

Thirty-four platelet imaging studies were performed in 23 patients to determine whether platelet deposition could be detected in patients with vascular aneurysms (18 patients) or in patients in whom Dacron prosthetic grafts had been place (5 patients). In patients in whom abnormal platelet deposition was detected, the effect of administration of platelet-active drugs on platelet deposition was examined. Of the 18 patients with an aneurysm, 12 had positive studies on initial imaging and 2 had equivocally positive images. Of five patients with Dacron arterial grafts in place, four had diffuse platelet deposition in the grafts; the fifth patient had platelet deposition only in a pseudoaneurysm. Eight patients with an abdominal aneurysm and positive or equivocally positive baseline images were restudied during platelet-active drug therapy either with aspirin plus dipyridamole (seven patients) or with sulfinpyrazone (four patients). No patient studied during treatment with aspirin plus dipyridamole had detectably decreased platelet deposition compared with baseline determinations. In contrast, two of four patients studied while receiving sulfinpyrazone showed decreased platelet deposition. Thus, platelet imaging may be of value for studying platelet physiology in vivo and for assessing platelet-active drugs and the thrombogenicity of prosthetic graft materials in human beings.

[Benign surgical icterus (author's transl)]

Among 3192 operations on the gall bladder and biliary ducts clinically and chemically a benign icterus was found in 318 patients (9.9%) (maximal serum bilirubin values 21 mumol/l). 140 patients (44%) had a typical biliary history over many years, 173 patients (54%) had only cholelithiasis, 98 patients (30.9%) had concrements in the gall bladder and biliary ducts and 9 patients (2.8%) had concrements in the biliary ducts only. In 141 patients (44.3%) additional complications were found. The post-operative mortality was 5% among which were 9 patients dying of the final stages of their basic disease or its complications; 7 patients died of cardiopulmonary complications. An improvement of the prognosis can only be reached by early operation of patients with gallstones.

[Number of spike-components contributing to the motor unit potential (author's transl)]

40 motor unit potentials recorded with concentric needle electrodes (Fig. 1) from the extensor digitorum communis muscle were analysed in order to find out the number of contributing muscle fibre action potentials. A "fractionation" of the motor unit potential was achieved by maintained voluntary activity under ischemic condition leading to a consecutive transmission block in the motor endplates within the active motor unit. Thus one after the other muscle fibre action potential failed to occur leading to a stepwise reduction of the motor unit potential which finally was abolished (Fig. 2 and 3). With technique it was shown that 65% of the area of the investigated motor unit potentials were composed of two to twelve (mean 5) muscle fibre action potentials (Fig 4). No correlation between the number of spike-components and duration or amplitude of the motor unit potential was found (Fig. 5). The non-analysed area of the motor unit potential probably represented activity of more distant muscle fibres of the motor unit.

Globin mRNA contains a sequence complementary to double-stranded region of nuclear pre-mRNA

Melted ds RNA isolated from rabbit bone marrow pre-mRNA was hybridized with excess of globin mRNA which was prepared from rabbit reticulocytes. 7-9% of ds sequences became RNAase-stable and about 30% of the sequences could be bound to poly(U)-Sepharose through poly (A) of mRNA. The size of RNAase-stable hybrid is about 30 nucleotides, that is one fourth of the length of one strand of the ds RNA.

The reinnervated motor unit in man. A single fibre EMG multielectrode investigation

Motor units in patients with motor neurone disease and polyneuropathy were studied with a new multielectrode technique allowing fibre mapping. In these disorders which are characterised by reinnervation the motor unit fibre distribution is changed from a normal scattered pattern to grouping often in clinically uninvolved muscles without definite EMG abnormalities. The changes found with this multielectrode technique in man are in accordance with those found in reinnervated motor units studied histochemically in the experimental animal.

The normal motor unit in man. A single fibre EMG multielectrode investigation

The motor unit in the normal EDC and biceps brachii muscle was studied with a multielectrode technique permitting recording from 44 sites 300 mum apart. It was found that the muscle fibres in man are scattered with no evidence of grouping, similar to the findings in glycogen depletion experiments in animals.

Ruptured iliac aneurysms

Iliac aneurysms are uncommon as compared with aneurysms of the abdominal aorta. Rupture is the most serious complication of aneurysms of both vessels. Considerable attention has been focused on the management of ruptured abdomonal aortic aneurysms, but ruptured iliac aneurysms have received little notice. The problems in the management of ten ruptured iliac aneurysms, seen over the last five years, together with the rarity of other reports of this condition, have stimulated this review.

Motor unit fibre density in the extensor digitorum communis muscle. Single fibre electromyographic study in normal subjects at different ages

A single fibre EMG study is presented from extensor digitorum communis muscle in sujbects aged 10 to 89 years. The average number of single muscle fibre action potentials generated by muscle fibres in the same motor unit within the uptake area of the electrode is used as a measure of the motor unit fibre density. The fibre density increases slowly during life with a faster progression after the age 70 years. The number of recordings indicating impaired nerve or neuromuscular impulse transmission increases at the same time. The findings indicate degenerative loss of motor neurones with aging, compensated for by reinnervation. The changes are relatively slight in the extensor digitorum communis muscle as compared with other muscles, permitting early pathological changes in this muscle to be recognized independently of age factors.

Single fibre EMG findings in polyneuropathies of different aetiology

Single fibre electromyography was carried out in patients with polyneuropathy due to uraemia, diabetes, and alcohol. In the two former groups the fibre density within the motor unit and the impulse transmission were mainly normal. In the latter group the fibre density was significantly increased as signs of reinnervation. Impulse transmission was impaired in a number of the action potential complexes, which is typical of active reinnervation. The results may indicate that the diabetic and uraemic polyneuropathies are characterized in the main by demyelination, whereas the alcoholic type is dominated by axonal lesion even at an early stage.

The bimodal jitter: a single fibre electromyographic finding

The jitter, obtained by SFEMG recordings, mainly reflects the neuromuscular transmission time variability and is usually Gaussian distributed. Here is reported the bimodal distribution of the interpotential intervals, the flip-flop phenomenon. Long flip-flop in cases of reinnervation may indicate alternatively continuous and saltatory nerve conduction. Short flip-flop in normal subjects may be due to muscle fibre interaction or nerve conduction irregularities.

Transmission block in terminal nerve twigs: a single fibre electromyographic finding in man

Single fibre electromyography has been performed in patients with partial nerve lesions, amyotrophic lateral sclerosis, progressive spinal muscle atrophy, muscular dystrophy, and distal hereditary myopathy. The recorded action potentials were often more complex than in the normal muscle due to increased fibre density in the motor unit and the individual spike components showed a large jitter and occasional blockings. Sometimes two or more spikes in a complex disappeared and reappeared simultaneously upon successive discharges. This phenomenon, called `paired blocking', has been further investigated. The jitter of the blocking potentials in relation to the rest of the complex was large, up to 500 μsec. The degree of blocking increased with increasing innervation frequency until it eventually proceeded to total block during continuous activity. Sometimes a slight effect on blocking was seen after edrophonium. This type of block is probably localized in the terminal nerve twigs, perhaps in newly formed sprouts. The phenomenon of neurogenic blocking may contribute to the fatigue clinically experienced in different denervation-reinnervation cases.