Stiff man syndrome: clinical and laboratory findings in eight patients

Stiff Person Spectrum Disorders-An Update and Outlook on Clinical, Pathophysiological and Treatment Perspectives

Stiff person spectrum disorders (SPSD) are paradigm autoimmune movement disorders characterized by stiffness, spasms and hyperekplexia. Though rare, SPSD represent a not-to-miss diagnosis because of the associated disease burden and treatment implications. After decades as an enigmatic orphan disease, major advances in our understanding of the evolving spectrum of diseases have been made along with the identification of multiple associated autoantibodies. However, the most important recent developments relate to the recognition of a wider affection, beyond the classic core motor symptoms, and to further insights into immunomodulatory and symptomatic therapies. In this review, we summarize the recent literature on the clinical and paraclinical spectrum, current pathophysiological understanding, as well as current and possibly future therapeutic strategies.

An Appraisal of Electrodiagnostic Studies in Stiff Person Syndrome

A literature review was performed on the use of electrodiagnostic (EDX) tests including nerve conduction study, electromyography, exteroceptive reflex, blink reflex, and late response in the evaluation of patients with stiff person syndrome (SPS). A web survey was conducted to report the extent of EDX testing usage in the evaluation of SPS among laboratories accredited by the American Academy of Neuromuscular and Electrodiagnostic Medicine. Coactivation of selected agonist and antagonist muscles was performed in 5 healthy subjects to determine its specificity for SPS. Observation of continuous motor unit activity on electromyography and elicitation of exteroceptive reflexes by electric stimulation are informative in assisting a diagnosis of SPS, but further studies focusing on their sensitivities in diagnosing SPS and specificities in differentiating SPS from other movement disorders are needed. The value of EDX testing in SPS lies in ruling out other neuromuscular disorders.

[From stiff man syndrome to stiff person spectrum disorders]

The identification of new variants of the stiff man syndrome (SMS) and of new, probably pathogenic neuronal autoantibodies has led to the concept of stiff man (or person) spectrum disorders (SPSD). This is an expanding group of rare chronic autoimmune inflammatory diseases of the central nervous system (CNS) that have in common the main symptoms of fluctuating rigidity and spasms with pronounced stimulus sensitivity. These core symptoms are mandatory and can be accompanied by a wide variety of other neurological signs. The SPSDs are associated with autoantibodies directed against neuronal proteins that attenuate excitability. Neither clinical phenotypes nor the course of SPSD correlate closely with the antibody status. The treatment of these diseases aims at maintaining mobility and is pragmatically oriented to the degree of impediment and comprises antispastic, anticonvulsant and immunomodulating or immunosuppressive medication strategies.

Anti-glutamic acid decarboxylase antibody positive neurological syndromes

A rare kind of antibody, known as anti-glutamic acid decarboxylase (GAD) autoantibody, is found in some patients. The antibody works against the GAD enzyme, which is essential in the formation of gamma aminobutyric acid (GABA), an inhibitory neurotransmitter found in the brain. Patients found with this antibody present with motor and cognitive problems due to low levels or lack of GABA, because in the absence or low levels of GABA patients exhibit motor and cognitive symptoms. The anti-GAD antibody is found in some neurological syndromes, including stiff-person syndrome, paraneoplastic stiff-person syndrome, Miller Fisher syndrome (MFS), limbic encephalopathy, cerebellar ataxia, eye movement disorders, and epilepsy. Previously, excluding MFS, these conditions were calledhyperexcitability disorders. However, collectively, these syndromes should be known as "anti-GAD positive neurological syndromes." An important limitation of this study is that the literature is lacking on the subject, and why patients with the above mentioned neurological problems present with different symptoms has not been studied in detail. Therefore, it is recommended that more research is conducted on this subject to obtain a better and deeper understanding of these anti-GAD antibody induced neurological syndromes.

Clinical and Immunologic Investigations in Patients With Stiff-Person Spectrum Disorder

IMPORTANCE

Symptoms of stiff-person syndrome (SPS), stiff-limb syndrome (SLS), or progressive encephalomyelitis with rigidity, myoclonus, or other symptoms (SPS-plus) can occur with several autoantibodies, but the relative frequency of each antibody, syndrome specificity, and prognostic implications are unclear.

OBJECTIVE

To report the clinical and immunologic findings of a large cohort of patients with stiff-person spectrum disorder (SPSD), including SPS, SLS, and SPS-plus.

DESIGN, SETTING, AND PATIENTS

This study retrospectively examined a case series (January 1, 1998, through December 31, 2014) of immunologic investigations performed in a neuroimmunology referral center. The study included 121 patients with clinical features of SPSD. Data analysis was performed from July 1, 2015, through November 1, 2015.

MAIN OUTCOMES AND MEASURES

Analysis of clinical-immunologic associations, including autoantibodies to 8 proteins expressed in inhibitory synapses.

RESULTS

The median age of the patients was 51 years (interquartile range, 40-61 years), and 75 (62.0%) were female. Fifty (41.3%) had SPS, 37 (30.6%) had SPS-plus, 24 (19.8%) had SLS, and 10 (8.3%) had SPS or SLS overlapping with ataxia, epilepsy, or encephalitis. Fifty-two patients (43.0%) had glutamic acid decarboxylase (GAD65) antibodies (2 with γ-aminobutyric acid-A [GABA-A] receptor antibodies), 24 (19.8%) had α1-subunit of the glycine receptor (GlyR) antibodies (2 with GAD65 antibodies), 5 (4.1%) had other antibodies, and 40 (33.1%) tested negative for antibodies. None had gephyrin or glycine transporter antibodies. Among the main immunologic groups (GAD65 antibodies, GlyR antibodies, and antibody negative), those with GAD65 antibodies were more likely to be female (45 [86.5%] of 52, 8 [36.4%] of 22, and 18 [45.0%] of 40, respectively; P < .001), have systemic autoimmunity (34 [65.4%] of 52, 7 [31.8%] of 22, and 13 [32.5%] of 40, respectively; P = .004), and have longer delays in being tested for antibodies (median, 3 vs 0.5 and 1 year; P < .001). Patients with GAD65 antibodies were more likely to develop SPS (27 [51.9%] of 52) or overlapping syndromes (8 [15.4%] of 52) than patients with GlyR antibodies (5 [22.7%] and 0 [0%] of 22, respectively), who more often developed SPS-plus (12 [54.5%] of 22 vs 7 [13.5%] in those with GAD65 antibodies); antibody-negative patients had an intermediate syndrome distribution. In multivariable analysis, symptom severity (P = .001) and immunologic group (P = .01) were independently associated with outcome. Compared with patients with GlyR antibodies, those with GAD65 antibodies (odds ratio, 11.1, 95% CI, 2.3-53.7; P = .003) had worse outcome. Patients without antibodies had similar outcome than patients with GlyR antibodies (odds ratio, 4.2, 95% CI, 0.9-20.0; P = .07).

CONCLUSIONS AND RELEVANCE

In SPSD, symptom severity and presence and type of antibodies are predictors of outcome.

A case of stiff dog syndrome associated with anti-glutamic acid decarboxylase antibodies

BACKGROUND

The stiff person syndrome (SPS) is a rare and debilitating autoimmune disorder with an unknown pathogenesis and variable clinical presentation that can present a diagnostic challenge. Although entities that clinically mimic stiff-person spectrum disorders (SPSD) have manifested in horses, they have not been reported in dogs.

CASE PRESENTATION

We describe a 2-year-old beagle dog presented for progressive attacks of muscular rigidity and lordosis with superimposed spasms of the appendicular muscles triggered by tactile stimulation which resulted in marked gait impairment. Resting electromyography revealed continuous motor unit activity in the axial musculature. Compared to age-matched healthy beagle dogs, this patient had elevated glutamic acid decarboxylase antibody concentrations in serum and cerebrospinal fluid.

CONCLUSION

This dog presented with phenotypic, electrodiagnostic, and immunologic criterion consistent with an SPSD, including elevated anti-GAD antibody titers, which we have termed the "stiff dog syndrome (SDS)". Durable clinical improvement was achieved with symptomatic and immunosuppressive treatments including baclofen, gabapentin, prednisone, and intravenous immunoglobulin.

Axial Dystonia Mimicking Stiff Person Syndrome

Both isolated axial dystonia and stiff person syndrome (SPS) are rare conditions that can look deceivingly similar. Here, we present three cases of axial dystonia resembling SPS with video documentation in order to illustrate the phenomenological similarities. We discuss clinical and paraclinical approaches to help distinction with its obvious implications for further management.

Autoimmune stiff person syndrome and related myelopathies: understanding of electrophysiological and immunological processes

Stiff person syndrome (SPS) is a disabling autoimmune central nervous system disorder characterized by progressive muscle rigidity and gait impairment with superimposed painful spasms that involve axial and limb musculature, triggered by heightened sensitivity to external stimuli. Impaired synaptic GABAergic inhibition resulting from intrathecal B-cell-mediated clonal synthesis of autoantibodies against various presynaptic and synaptic proteins in the inhibitory neurons of the brain and spinal cord is believed to be an underlying pathogenic mechanism. SPS is most often idiopathic, but it can occur as a paraneoplastic condition. Despite evidence that anti-GAD and related autoantibodies impair GABA synthesis, the exact pathogenic mechanism of SPS is not fully elucidated. The strong association with several MHC-II alleles and improvement of symptoms with immune-modulating therapies support an autoimmune etiology of SPS. In this review, we discuss the clinical spectrum, neurophysiological mechanisms, and therapeutic options, including a rationale for agents that modulate B-cell function in SPS.

Human stiff-person syndrome IgG induces anxious behavior in rats

Background

Anxiety is a heterogeneous behavioral domain playing a role in a variety of neuropsychiatric diseases. While anxiety is the cardinal symptom in disorders such as panic disorder, co-morbid anxious behavior can occur in a variety of diseases. Stiff person syndrome (SPS) is a CNS disorder characterized by increased muscle tone and prominent agoraphobia and anxiety. Most patients have high-titer antibodies against glutamate decarboxylase (GAD) 65. The pathogenic role of these autoantibodies is unclear.

Methodology/Principal Findings

We re-investigated a 53 year old woman with SPS and profound anxiety for GABA-A receptor binding in the amygdala with (11)C-flumazenil PET scan and studied the potential pathogenic role of purified IgG from her plasma filtrates containing high-titer antibodies against GAD 65. We passively transferred the IgG fraction intrathecally into rats and analyzed the effects using behavioral and in vivo electrophysiological methods. In cell culture, we measured the effect of patient IgG on GABA release from hippocampal neurons. Repetitive intrathecal application of purified patient IgG in rats resulted in an anxious phenotype resembling the core symptoms of the patient. Patient IgG selectively bound to rat amygdala, hippocampus, and frontal cortical areas. In cultured rat hippocampal neurons, patient IgG inhibited GABA release. In line with these experimental results, the GABA-A receptor binding potential was reduced in the patient's amygdala/hippocampus complex. No motor abnormalities were found in recipient rats.

Conclusion/Significance

The observations in rats after passive transfer lead us to propose that anxiety-like behavior can be induced in rats by passive transfer of IgG from a SPS patient positive for anti-GAD 65 antibodies. Anxiety, in this case, thus may be an antibody-mediated phenomenon with consecutive disturbance of GABAergic signaling in the amygdala region.

Progressive encephalomyelitis with rigidity: a case report

BACKGROUND/OBJECTIVE

The most prominent clinical features of progressive encephalomyelitis with rigidity (PER) are painful spasms and rigidity accompanied by clinical signs of brainstem and spinal cord involvement. In initial reports, PER had fatal outcome. Later, clinical improvement related to corticosteroid therapy has been described in some cases. The objective of this study was to signify a reputed clinical significance of corticosteroid therapy in PER.

METHODS

Case report.

RESULTS

A 50-year-old man developed progressive syndrome of tonic extensor spasms. Magnetic resonance imaging (MRI) showed areas of signal changes in cervical spinal cord and lower brainstem, whereas cerebrospinal fluid analysis indicated subacute encephalomyelitis. His condition dramatically improved on oral corticosteroid therapy. Clinical improvement was accompanied by normalization of MRI findings.

CONCLUSION

For this patient with PER, corticosteroid therapy was a dramatically effective and life-saving treatment, although initiated rather late in the course of the disease.

Stiff-person syndrome with acute recurrent peripheral vertigo: possible evidence of gamma aminobutyric acid as a neurotransmitter in the vestibular periphery

OBJECTIVE

We report a case of a 58-year-old man suffering from stiff-person syndrome and recurrent peripheral vertigo.

METHOD

A case report and a review of the recent literature on stiff-person syndrome are presented.

RESULTS

The patient presented with recurrent episodes of vertigo with a pure peripheral pattern and with concomitant episodes of burning muscle pain, muscle twitching, weight gain and fatigue, worsening with tension or stress that also occurred in periods without vertigo. Cochlear examinations only showed presbyacusis-like hearing loss. The diagnosis of stiff-person syndrome was made with electromyographic examination and from findings in the blood and cerebrospinal fluid of high titres of anti-glutamic acid decarboxylase (GAD67) autoantibodies. In a two-year follow-up period, therapy for stiff-person syndrome abolished episodes of both stiffness and vertigo.

CONCLUSION

As far as we know, no other clinical case of acute vestibular damage with a possible correlation with anti-glutamic acid decarboxylase antibodies has been described. Peripheral vertigo possibly related to a lack of gamma aminobutyric acid underlines a possible role of gamma aminobutyric acid as a neurotransmitter in the peripheral vestibular system.

Selective loss of Purkinje cells in a patient with anti-glutamic acid decarboxylase antibody-associated cerebellar ataxia

Anti-glutamic acid decarboxylase antibody is associated with the development of progressive cerebellar ataxia and slowly progressive insulin-dependent diabetes mellitus. Previously, the neurophysiological characteristics of IgG in the cerebrospinal fluid of a patient with anti-glutamic acid decarboxylase antibody-associated progressive cerebellar ataxia and slowly progressive insulin-dependent diabetes mellitus were reported. Using a voltage-gated whole-cell recording technique, it was observed that the IgG in the cerebrospinal fluid of the patient selectively suppressed the inhibitory postsynaptic currents in the Purkinje cells. The patient died from aspiration pneumonia. Postmortem examination showed almost complete depletion of the Purkinje cells with Bergmann gliosis. Therefore, the main cause of cerebellar ataxia observed in this case may be attributed to the near-complete depletion of the Purkinje cells. In this paper, the pathomechanisms underlying Purkinje cell damage are discussed.

Glutamic acid decarboxylase autoimmunity with brainstem, extrapyramidal, and spinal cord dysfunction

OBJECTIVE

To describe novel neurological manifestations associated with glutamic acid decarboxylase (GAD65) autoimmunity.

PATIENTS AND METHODS

This retrospective study (1987-2003) describes 62 patients Incidentally found to have a serum autoantibody that bound selectively to synapse-rich central nervous system tissues. The immunostaining pattern was determined to be GAD65-specific by radiolmmunoprecipitation assay. These cases were identified among samples submitted for paraneoplastic autoantibody evaluation using indirect immunofluorescence. In no case had GAD65 or any other islet cell antibody testing been requested.

RESULTS

In most cases, the patients' presentations were initially considered neurodegenerative or inflammatory (multiple sclerosis or paraneoplastic). Median age at onset was 50 years, and 77% were women. Of the 44 patients seen at the Mayo Clinic, 23% were African American; in contrast, less than 10% of Mayo Clinic's neurology patients are African American. Median follow-up was 24 months. The radioimmunoprecipitation assay values for GAD65 antibody were extremely high (median, 1429 nmol/L; Interquartile range, 643-3078 nmol/L) and correlated significantly with immunofluorescence titers (median, 3840; interquartile range, 1920-15,360; r = 0.81; P < .001). Neurological manifestations were multifocal in 41 patients and included cerebellar ataxia (63%), brainstem involvement (29%), seizures (27%), stiff-man phenomena (26%), extrapyramidal signs (16%), and myelopathy (8%). One third of the patients had type 1 diabetes mellitus, 53% had thyroid autoantibodies, and 16% had vitiligo. Eleven of 20 patients identified as African American had brainstem involvement. Some patients appeared to benefit from short-term immunosuppression (none received long-term therapy).

CONCLUSIONS

The neurological spectrum of GAD65 autoimmunity includes brainstem, extrapyramidal, and spinal cord syndromes. In our experience, African American patients were disproportionately affected. A patient with a presumed neurodegenerative disorder of new onset, with high levels of GAD65 antibody (>20 nmol/L), merits consideration of immunotherapy.

Potential Role of Anti-GAD Antibodies in Abnormal Eye Movements

Glutamic acid decarboxylase (GAD) catalyzes the conversion of glutamic acid to gamma-aminobutyric acid (GABA). Autoantibodies directed against GAD (antiGAD-Ab) have been described in patients with insulin-dependent diabetes mellitus, stiff-man syndrome, and in a few patients with progressive cerebellar ataxia. The presence of these autoantibodies suggests an autoimmune pathophysiological mechanism for the neurological manifestations in these disorders. However, the exact role of antiGAD-Ab and GABAergic neurotransmission in the pathogenesis of the neurological manifestations, particularly in progressive cerebellar ataxia, is not fully understood. The cases of two patients with subacute cerebellar ataxia associated with antiGAD-Ab presenting with abnormal eye movements are reported. One patient presented a periodic alternating nystagmus (PAN), whereas the other presented a downbeat nystagmus (DBN) and slow vertical saccades. The potential role of antiGAD-Ab and the resultant GABAergic neurotransmission deficit in oculomotor manifestations is discussed.

Stiff-person syndromes: motor cortex hyperexcitability correlates with anti-GAD autoimmunity

OBJECTIVE

S: To investigate whether motor cortex excitability is enhanced in both stiff-person syndrome (SPS) and its "plus" variant, progressive encephalomyelitis with rigidity (PER), and related to autoimmunity against glutamic acid decarboxylase (GAD).

METHODS

The authors compared 21 patients with SPS or PER (7 untreated, 14 treated) with 14 age-matched healthy controls and used transcranial magnetic stimulation (TMS, paired-pulse paradigm) to investigate intracortical inhibition (ICI) and intracortical facilitation (ICF). GAD autoantibody levels in serum and CSF were determined by radioimmunoassay.

RESULTS

The authors found significantly enhanced motor cortex excitability in untreated SPS and PER patients. GABAmimetic medication significantly reduced ICF but did not affect ICI. Motor cortex excitability was more enhanced in patients with GAD antibodies than in patients without GAD antibodies and correlated positively with GAD antibody levels in CSF.

CONCLUSIONS

The motor cortex is hyperexcitable in SPS and PER patients. However, hyperexcitability is partly masked by GABAmimetic treatment. Correlation of elevated GAD antibody levels with enhanced ICF suggests that motor cortex hyperexcitability in SPS and PER is related to anti-GAD autoimmunity.

Head retraction reflex in stiff-man syndrome and related disorders

The head retraction reflex (HRR) is a vestigial withdrawal reflex of the face and is suppressed in healthy subjects. We investigated the prevalence and electrophysiological patterns of the HRR in patients suffering from stiff-man syndrome (SMS, n = 28) and related disorders, stiff-limb syndrome (SLS, n = 2), and progressive encephalomyelitis with rigidity and myoclonus (PERM, n = 20). In patients with a positive HRR, the electromyographic (EMG) pattern was analyzed with surface recordings from the orbicularis oculi, sternocleidomastoid, trapezius, and the paraspinal extensor muscles at midthoracic and lumbar levels. On clinical testing, 17 of 28 SMS patients, 10 of 20 PERM patients, and 0 of 2 SLS patients had a positive HRR, ranging from a brief contraction of the neck extensors to violent retropulsion of the upper body. In all muscles, EMG reflex patterns elicited by gentle taps to the face or by electrical stimulation of the trigeminal nerve branches consisted of two components: an early, synchronous, brief burst with the shortest latency in trapezius (12.5-20.0 msec) and a late, asynchronous, longer response with latencies between 44 and 70 msec. We conclude that the HRR is an abnormal cutaneomuscular brainstem reflex that occurs in a considerable proportion of patients with SMS and related disorders. Although neither specific nor particularly sensitive for SMS, presence of the HRR in a setting with otherwise unexplained stiffness and spasms might help to avoid the otherwise frequent misdiagnosis of a psychogenic motor disturbance in patients with SMS.

Stiff man syndrome and related conditions

The stiff man syndrome (SMS) and its variants, focal SMS, stiff limb (or leg) syndrome (SLS), jerking SMS, and progressive encephalomyelitis with rigidity and myoclonus (PERM), appear to occur more frequently than hitherto thought. A characteristic ensemble of symptoms and signs allows a tentative clinical diagnosis. Supportive ancillary findings include (1) the demonstration of continuous muscle activity in trunk and proximal limb muscles despite attempted relaxation, (2) enhanced exteroceptive reflexes, and (3) antibodies to glutamic acid decarboxylase (GAD) in both serum and spinal fluid. Antibodies to GAD are not diagnostic or specific for SMS and the role of these autoantibodies in the pathogenesis of SMS/SLS/PERM is the subject of debate and difficult to reconcile on the basis of our present knowledge. Nevertheless, evidence is emerging to suggest that SMS/SLS/PERM are manifestations of an immune-mediated chronic encephalomyelitis and immunomodulation is an effective therapeutic approach.

Stiff-man syndrome: identification of 17 beta-hydroxysteroid dehydrogenase type 4 as a novel 80-kDa antineuronal antigen

Stiff-man syndrome (SMS) is a rare autoimmune disorder of the central nervous system associated with autoantibodies to glutamate decarboxylase (GAD). We isolated five brain-reactive human monoclonal antibodies, with reactivity distinct from GAD, from peripheral blood of a patient newly diagnosed with SMS. Two antibodies reacted with both Purkinje cells and ependymal cells, and precipitated an 80-kDa protein from rat neuronal primary cultures, which was also recognized by 12% (3/25) of SMS sera and 13% (2/15) of SMS cerebrospinal fluid (CSF) samples. The corresponding antigen was identified as 17 beta-hydroxysteroid dehydrogenase type 4 and may represent a possible novel target of autoimmunity in SMS.

Pathological evidence of encephalomyelitis in the stiff man syndrome with anti-GAD antibodies

We report the case of a 57 year old woman with typical clinical features of the stiff man syndrome (SMS) and antibodies to glutamic acid decarboxylase (antiGADAb), who developed a supranuclear gaze palsy, ileus and died of bronchopneumonia eight years after the onset of illness. Post mortem examination revealed perivascular lymphocyte cuffing throughout the cerebral hemispheres, brainstem and spinal cord and neuronal loss in medial anterior horns of the cervical spinal cord. These findings support the notion that the SMS and progressive encephalomyelitis with rigidity (PER) form a clinical and pathologic continuum.

Progressive encephalomyelitis with rigidity presenting as a stiff-person syndrome

Diagnosis criteria of stiff-person syndrome (SPS) include progressive, fluctuating muscular rigidity and spasms with normal neurological examination. The presence of unusual features such as prominent limb rigidity with segmental signs and contracture, evidence of brainstem dysfunction, profound autonomic disturbances, CSF pleiocytosis or MRI abnormalities in patients with SPS presentation allows to classify these patients as progressive encephalomyelitis with rigidity (PER). We report a 50 year-old woman suffering from severe painful spasms of abdominal wall and limb muscles. Neurological examination showed pyramidal signs. EMG disclosed continuous muscle activity with superimposed discharges. Treatment with high doses of diazepam and baclofen led to moderate improvement of generalised stiffness. However, the right arm became more rigid with oedema and vasomotor changes. Subsequently, bilateral nystagmus and internuclear opthalmplegia appeared. There was mild CSF pleiocytosis. Associated auto-immune thyroiditis was found with positive anti-microsome antibodies and decreased thyroid hormones. Search for profound neoplasm was negative. The patient had three subacute bouts then she improved with methylprednisolone. The initial clinical presentation mimicking a SPS with subsequent diffuse involvement of the central nervous system and a striking localisation of a severe rigidity to one arm allowed to suspect the diagnosis of PER. The relationship between SPS and PER remains unclear because of the rarity of these disorders. The observation reported in this paper gives evidence that both the disorders are probably two clinical presentations of the same pathogenic process.

Atypical low back pain: stiff-person syndrome

Stiff-person syndrome was diagnosed in a patient with chronic low back pain. The diagnosis of this rare neurological condition rests mainly on the clinical findings of axial and proximal limb rigidity, increased lumbar lordosis often accompanied with pain, and normal neurological findings apart from brisk deep tendon reflexes. Electromyography of the lumbar paraspinal muscles shows motor unit firing at rest with normal appearance of the motor unit potentials. Titers of antibody to glutamic acid decarboxylase are elevated. Diazepam is the treatment of reference. Physical therapy can substantially improve quality of life.

Stiff man syndrome

Stiff man syndrome (SMS), an uncommon neurological disease, is characterised by symmetrical muscle stiffness and spasms that often lead to skeletal deformity. Variants of the syndrome may involve one limb only (stiff leg syndrome), a variety of additional neurological symptoms and signs such as eye movement disturbances, ataxia, or Babinski signs (progressive encephalomyelitis with rigidity and myoclonus), or be associated with malignant disease (paraneoplastic SMS). Antineuronal autoimmunity and accompanying autoimmune diseases, most often insulin-dependent diabetes mellitus, are characteristic features of SMS and its variants. The condition is frequently misinterpreted as psychogenic movement disturbance, but electromyographic abnormalities and the presence of autoantibodies against glutamic acid decarboxylase (GAD) in both serum and cerebrospinal fluid help to establish the correct diagnosis. The aetiology of SMS is obscure. However, several features suggest that SMS is an autoimmune-mediated chronic encephalomyelitis. In line with this hypothesis, immunomodulation with a front-loaded methylprednisolone regimen reduces stiffness and spasms and improves other neurological symptoms in the majority of patients. Plasmapheresis or intravenous immunoglobulins are effective less frequently. For symptomatic treatment, the benzodiazepines are drugs of first choice. An alternative of last resort is baclofen administered intrathecally via an implanted pump device.

Stiff leg syndrome: case report

We report on a 28-year-old woman with insulin-resistant diabetes mellitus with a 5-year history of progressive stiffness and painful spasms of the right leg, exaggerated by sudden auditory and tactile stimuli or by emotional stress. There were no signs of truncal rigidity or exaggerated lumbar lordosis. Anti-glutamic acid decarboxylase antibodies were positive in her serum. She improved substantially with clonazepam 4 mg/day. She presented with electrophysiological findings not previously reported in stiff leg syndrome, which may suggest increased inhibition in the uninvolved upper extremities.

The stiff-man syndrome and related disorders

The stiff-man syndrome (SMS) is characterised by rigidity and spasm of predominantly axial and proximal limb muscles. The cause of the condition is unknown but the finding of antibodies to glutamic acid decarboxylase (GAD) in approximately 60% of patients has suggested an autoimmune basis. Pathological findings are limited to a small number of cases which are reviewed in this paper. In some, evidence of an inflammatory aetiology has been found, and there appears to be overlap with progressive encephalomyelitis with rigidity (PER) which may present with a similar clinical picture. The spontaneous muscle activity in SMS and PER is of central origin, related to release of polysynaptic spinal and brainstem reflexes. The SMS is readily distinguished from the continuous muscle activity, spasm and cramps of Isaac's syndrome and neuromyotonia which originate in the peripheral nervous system. Fasciculations, myokymia, myotonia and complex repetitive discharges are characteristic of these peripheral neuromuscular disorders.

Motor cortex excitability in stiff-person syndrome

Muscle stiffness in stiff-person syndrome (SPS) is produced by continuous, involuntary firing of motor units that is thought to be caused by an autoimmune mediated dysfunction of GABA-ergic inhibitory neurones. We have postulated that the loss of GABA-ergic inputs from spinal interneurones alone is insufficient to produce tonic firing of motor neurones and that excessive supraspinal excitation could also play a role. To determine whether SPS is associated with dysfunction in supraspinal GABA-ergic neurones, we assessed the excitability of the motor cortex with transcranial magnetic stimulation (TMS) in seven SPS patients and seven age-matched healthy volunteers. SPS patients had normal central motor conduction times, normal thresholds for motor evoked potentials (MEPs) in leg muscles, and a normal MEP stimulus versus response recruitment curve with increasing TMS intensities in resting hand and leg muscles. Cortical silent periods were shortened in leg muscles. Intracortical inhibition and excitation were assessed while recording from the abductor pollicis brevis, using a paired pulse TMS paradigm with subthreshold conditioning stimuli. Patients had decreased inhibition and markedly increased facilitation at short intervals. Using paired suprathreshold TMS, patients exhibited increased facilitation at 20- and 40-ms intervals. These results point to a hyperexcitability of the motor cortex in SPS, which could be explained by impairment of supraspinal GABA-ergic neurones, leading to an impaired balance between inhibitory and excitatory intracortical circuitry.

The stiff-person syndrome: an autoimmune disorder affecting neurotransmission of gamma-aminobutyric acid

The stiff-person syndrome, a rare and disabling disorder, is characterized by muscle rigidity and episodic spasms that involve axial and limb musculature. Continuous contraction of agonist and antagonist muscles caused by involuntary motor-unit firing at rest are the hallmark clinical and electrophysiologic signs of the disease. Except for global muscle stiffness, results of neurologic examination are usually normal. Results of conventional computed tomography and magnetic resonance imaging of the brain are also normal. The cause of the stiff-person syndrome is unknown; however, an autoimmune pathogenesis is suspected because of 1) the presence of antibodies against glutamic acid decarboxylase (GAD), the rate-limiting enzyme for the synthesis of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA); 2) the association of the disease with other autoimmune conditions; 3) the presence of various autoantibodies; and 4) a strong immunogenetic association. Anti-GAD antibodies, which are found in high titers in most patients, seem to be directed against conformational forms of GAD. New evidence suggests that these antibodies may be pathogenic because they interfere with the synthesis of GABA. In addition, a reduction in brain levels of GABA, which is prominent in the motor cortex, has been demonstrated with magnetic resonance spectroscopy in patients with the stiff-person syndrome. The stiff-person syndrome is clinically elusive but potentially treatable and should be considered in patients with unexplained stiffness and spasms. Drugs that enhance GABA neurotransmission, such as diazepam, vigabatrin, and baclofen, provide mild to modest relief of clinical symptoms. Immunomodulatory agents, such as steroids, plasmapheresis, and intravenous immunoglobulin, seem to offer substantial improvement. Results of an ongoing controlled trial will elucidate the role of these agents in the treatment of the disease.

Stiff-man syndrome: from the bedside to the bench

The study of SMS, a rare disease, has resulted in a better understanding of a more common disorder, IDDM, and has allowed investigators to gain insights into the molecular mechanisms of autoimmunity. Many unanswered questions remain, such as the specific site of disease activity in SMS, both at the bedside (cortex, brain stem, or spinal cord) and at the bench (neuronal cytoplasma or synapse). The association of SMS with neoplastic disease and the development of autonomicdysfunction are not understood. The next decade may provide answers to these puzzling issues.

Stiff-man syndrome

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Inhibition of gamma-aminobutyric acid synthesis by glutamic acid decarboxylase autoantibodies in stiff-man syndrome

Stiff-man syndrome (SMS) is a rare disorder of the central nervous system thought to result from an impairment of gamma-aminobutyric acid (GABA)ergic neurotransmission. Autoantibodies to the GABA-synthesizing enzyme glutamic acid decarboxylase (GAD), present in about 60% of SMS patients, have suggested an autoimmune pathogenesis of SMS. By using serum or cerebrospinal fluid from 25 SMS patients, we assessed the effect of GAD autoantibodies (GAD-A) on GAD enzymatic activity in vitro; 83% of GAD-A-positive SMS sera reduced GABA production in crude rat cerebellar extracts, whereas GAD-A- sera from SMS patients or healthy blood donors did not alter the enzyme activity. Inhibition of GABA synthesis by SMS sera was dose dependent and mediated by the purified IgG fraction of the sera. Human monoclonal GAD65-A and IgG purified from serum of GAD-A-positive patients with insulin-dependent diabetes or autoimmune polyendocrine syndrome did not affect GAD activity, suggesting that a specific epitope recognition of GAD-A mediates inhibition of GAD. The disease-specific detection of GAD-inhibitory antibodies is compatible with their functional involvement in the etiopathology of SMS; the relevance of such antibodies in vivo, however, remains to be determined.

Stiff-leg syndrome: a focal form of stiff-man syndrome

We report on 2 patients who presented stiffness and spasms similar to those of stiff-man syndrome (SMS) that were limited to one leg for up to 11 years. Patients had serum glutamic acid decarboxylase (GAD) autoantibodies in high titer, clinical evidence of organ-specific autoimmunity, and electromyographic pattern of continuous motor unit activity with abnormally enhanced exteroceptive reflexes. The clinical and immunological profile suggests that this disorder may be a focal form of SMS.

Stiff-man syndrome. Results of interviews and psychologic testing

Thirteen patients with stiff-man syndrome (SMS) were studied with the Minnesota Multiphasic Personality Inventory (MMPI), the Self-Administered Alcoholism Screening Test (SAAST), the State-Trait Anxiety Inventory (STAI) profiles, and by telephone interviews. The mean MMPI, SAAST, and STAI were within normal limits; however, several patients had abnormal profiles. The results of telephone interviews revealed that 8 patients (62%) had been given at least 1 psychiatric diagnosis and 4 (31%) abused alcohol or were dependent on it. Two patients had a psychiatric diagnosis that preceded the onset of symptoms of SMS. The authors hypothesize that SMS patients have a gamma-aminobutyric acid deficiency or GABAergic neuron dysfunction that leads to psychiatric symptoms, including depression and chemical abuse. Clinicians treating patients with SMS must be alert to the possible presence of comorbid psychiatric illnesses in this patient population.

Antibodies to the tyrosine phosphatase-like protein IA-2 are highly associated with IDDM, but not with autoimmune endocrine diseases or stiff man syndrome

Antibodies to the 40 kD antigen (identified as tyrosine phosphatase IA-2) and glutamate decarboxylase (GAD65) are strongly associated with insulin dependent diabetes mellitus (IDDM). However, antibodies to GAD (GADA) can appear in the absence of IDDM, particularly in stiff man syndrome (SMS) and in some individuals with autoimmune polyendocrine syndrome type II (APS II) and organ specific autoimmune diseases. The aim of this study was to compare the specificity of IA-2 antibodies (IA-2A) and GADA for IDDM by determining their frequency in different patient groups. IA-2A were present in 64/114 (56%) IDDM patients and 9/19 (47%) APS II patients with IDDM but in only 4/28 (14%) SMS patients. 1/24 (4%) APS II patients without IDDM and 1/113 (0.9%) patients with organ specific autoimmune disease had low level IA-2A. In contrast GADA were present in 77/114 (68%) IDDM patients and 17/19 (89%) APS II patients with IDDM, but also in 25/28 (89%) SMS patients, 5/24 (21%) APS II patients without IDDM and 22/113 (19%) patients with organ specific autoimmune diseases. Furthermore, within the group of new onset IDDM, IA-2A seemed to be associated with ICA and age: 63% of ICA positive IDDM patients had IA-2A (74% had GADA) increasing to 77% in the group below 20 years of age (69% for GADA). Our results demonstrate that IA-2A may be more specific for IDDM than GADA, as the latter are also present in patients with SMS, APS II without IDDM and organ specific autoimmune diseases. IA-2A were less frequent in older patients with IDDM than GADA or ICA. A combination of IA-2A and GADA detected 84% of total and 93% of ICA positive IDDM patients.

Motor neuron disease following generalized fasciculations and cramps

We report a case of motor neuron disease in which fasciculations and cramps progressed generally before the development of muscle wasting. After involvement of the upper and lower motor neurons became clinically manifest, widespread fasciculations and cramps persisted and accompanied pseudotetany. The present case suggests that spinal cord pathology of motor neuron disease can cause the abnormal excitability of the motor neurons, resulting in the development of generalized fasciculations and cramps.

A new variant of progressive encephalomyelitis with rigidity associated with cerebellar ataxia and dementia: correlation of MRI and histopathological changes. A case report

A 27 year-old patient developed a progressive neurological multisystem disorder. Initial signs were cerebellar ataxia and dementia, followed by rigidity and oculomotor dysfunction. Myoclonus was not present. MRI showed a marked atrophy of the spinal cord, the cerebellum, and mild (sub)cortical atrophy. CSF contained oligoclonal bands, but no anti-glutamic acid dehydrogenase antibodies. He died 33 months after onset of symptoms. Autopsy revealed widespread neuropathological alterations including perivascular lymphocytic cutting, neuronal cell loss, and micro/astrogliosis the distribution of which corresponded to the changes seen in MRI. The diagnosis of progressive encephalomyelitis with rigidity was pathohistologically confirmed. Brain samples were negative for neurotrophic viruses tested by polymerase chain reaction. A new variant of this rare disorder is described initially presenting with ataxia and dementia, but without myoclonus.

Brainstem encephalopathy with stimulus-sensitive myoclonus leading to respiratory arrest, but with recovery: a description of two cases and review of the literature

Two unrelated patients developed bulbar symptoms, followed within several weeks by spontaneous myoclonus and painful, generalized, stimulus-sensitive jerks triggered by unexpected noises and cutaneous stimuli. They progressed to respiratory arrest and required mechanical ventilation, but both patients subsequently made an almost full recovery. These cases stress the importance of persevering with supportive treatment despite rapid progression of this severe generalized movement disorder. The relationship of brainstem reflex myoclonus to hyperekplexia, progressive encephalomyelitis with rigidity, and the stiff-man syndrome is discussed.

Mapping of an autoreactive epitope within glutamate decarboxylase using a diabetes-associated human monoclonal autoantibody and an epitope cDNA library

Glutamate decarboxylase (GAD65) is a major autoantigen in insulin-dependent diabetes (IDDM) and the neurological disorder Stiff-Man-Syndrome (SMS). We derived a human monoclonal autoantibody (MICA 2) from peripheral blood of a patient newly diagnosed with IDDM, which reacted with GAD65 in Western blots. This indicated that a linear epitope is recognized by MICA 2. Using an epitope cDNA library we mapped the MICA 2 epitope to a contiguous stretch of 26 amino acids (506-531) in the C-terminus of GAD65. Neither blocking experiments with synthetic peptides nor analysis of overlapping decapeptides expressed as fusion proteins allowed us to further narrow down the epitope to the typical size of linear epitopes of 6-8 amino acids. We suggest that a miniconformational epitope provided by amino acids 506-531 is recognized by MICA 2, which withstands SDS gel electrophoresis without destruction or partially refolds during the Western blot procedure. A sequence homology with human heat shock protein 60 (HSP60) maps to this region of GAD65 but no cross-reactivity of MICA 2 with HSP60 occurred. Our data demonstrate that reactivity of an antibody in Western blots does not necessarily define a classic linear epitope of 6-8 amino acids and describe a new autoreactive epitope in GAD65 different from those reported for sera from patients with SMS.

Stiff-person syndrome with anti-glutamic acid decarboxylase autoantibodies: complete remission of symptoms after intrathecal baclofen administration

A female patient, aged 61 years, who developed a severe immobilizing stiff-person syndrome in conjunction with insulin-dependent diabetes mellitus, is described. In addition to the typical clinical symptoms, diagnosis was proven by the presence of autoantibodies against glutamic acid decarboxylase in serum and cerebrospinal fluid. Symptomatic treatment with continuous intrathecal application of baclofen administered by a subcutaneous pump resulted in rapid clinical improvement so that the patient became ambulatory. Intermittent withdrawal from intrathecal baclofen therapy led to complete remanifestation of stiff-person syndrome within 18 h; after re-introduction of intrathecal therapy stiffness disappeared completely within 48 h. The clinical course has been stable now for over 24 months and stiffness has completely disappeared. The effect of baclofen in this patient is discussed in the light of the suggested pathophysiological mechanisms in stiff-person syndromes.

Stiff man syndrome: neurophysiological findings in eight patients

The neurophysiological findings in eight patients with the stiff man syndrome (SMS), including four of six tested with autoantibodies against glutamic acid decarboxylase, are presented. Neurophysiological findings did not make it possible to discriminate between patients with and those without autoimmunity against GABAergic neurons. Investigation of mono- and polysynaptic reflexes revealed abnormal results in a variable number of SMS patients, the abnormalities largely corresponding to those seen in spastic paresis. A stereotyped motor response to electrical stimulation of peripheral nerves was recorded from the trunk muscles of all patients investigated. This response was termed spasmodic reflex myoclonus and consisted of a sequence of 1-3 synchronous myoclonic bursts, 60-70 ms after median nerve stimulation, followed by a tonic decrescendo activity over a number of seconds. The recruitment order of muscles along the neuraxis in spasmodic reflex myoclonus suggested that the latter was generated in the spinal cord and conveyed via propriospinal tracts. It is thought that spasmodic reflex myoclonus may serve not only as a diagnostic tool, but also as a key to understanding some aspects of the pathophysiology of both spasms and stiffness in SMS. It is speculated that stiffness is a fragment of spasms, both being generated by common neuronal mechanisms tentatively ascribed to interneurons in the spinal grey matter.