Ocular myasthenia gravis associated with x-linked recessive spinal and bulbar muscular atrophy

Kennedy’s disease presented with mastication fatigue combined with positive titin antibody: a case report

Background

Spinal and bulbar muscular atrophy (SBMA) is an X-linked recessive hereditary neuromuscular disorder caused by the expanded trinucleotide repeat in the androgen receptors gene. The major clinical manifestations of SBMA consist of weakness in the bulbar and limb muscles, fasciculations, tremors, cramps, sensory impairment, and gynecomastia. However, atypical SBMA cases may lead to misdiagnosis. Muscular fatigue and decremental responses to repetitive nerve stimulation (RNS), despite being observed in some SBMA patients, are usually occurred in MG patients, and patient with the symptom of mastication fatigue was rarely reported. In addition, cardiological investigations have been performed in SBMA patients and several ECG alterations were identified. Here we report an SBMA patient presenting with a rare onset symptom of mastication fatigue, who has been detected with a positive titin antibody in the serum and showed a WPW pattern electrocardiogram.

Case presentation

The patient showed mildly progressive fatigue in the muscles of mastication over 3 years. Neurological examination showed facial muscle weakness and a wasting tongue with fasciculations, but the weakness, wasting, or fasciculations were not obvious in the limbs. 3-Hz RNS showed a decremental response in bilateral orbicularis oculi. The test of titin antibody was positive in the serum, and the electrocardiogram showed a WPW pattern ECG. Genetic analysis revealed an increased number (39 repeats) of tandem CAG repeats in the AR gene, which confirmed the diagnosis of SBMA. The fatigue symptom was significantly improved after oral pyridostigmine bromide treatment.

Conclusion

This case calls for more attention to muscular fatigue as the onset symptoms of Kennedy’s disease. ECG screening is of importance in SBMA patients and further studies are needed to investigate the titin antibody in SBMA patients as well as other neurogenic disorders.

Acetylcholinesterase inhibitor responsive myasthenia in a Filipino male with X-linked recessive spinal and bulbar muscular atrophy

We report a 51-year-old male diagnosed with X-linked recessive spinal and bulbar muscular atrophy (SBMA) by genetic testing who presented with 30 years history of progressive proximal and bulbar weakness responsive to cholinesterase inhibitor. Although the anti-acetylcholine receptor antibody (anti-AChR Ab) was negative, the myasthenic state was confirmed by decremental response in repetitive nerve stimulation and increased jitter frequency and blocking in single fiber-electromyography. While myasthenia gravis and SBMA may co-exist independently in an individual having the signs and symptoms of both conditions, the absence of anti-AChR Ab may imply that myasthenia can be an exaggerated activity-induced fatigue or weakness from the latter.

Decremental responses to repetitive nerve stimulation in x-linked bulbospinal muscular atrophy

BACKGROUND AND PURPOSE

X-linked bulbospinal muscular atrophy (X-BSMA) is characterized by bulbar and spinal muscular weakness and fasciculations. Although X-BSMA is a motor neuronopathy, there are several reports of myasthenic symptoms or decremental responses to repetitive nerve stimulation (RNS). We report the results of applying the RNS test to 15 patients among 41 with genetically confirmed X-BSMA; these 15 patients complained of fatigue, ease of becoming tired, or early muscular exhaustion.

METHODS

The 3-Hz RNS test was performed on the trapezius, nasalis, orbicularis oculi, flexor carpi ulnaris, and abductor digiti quinti muscles. A decrement greater than 10% was considered abnormal. Additionally, a pharmacologic response to neostigmine was identified in three patients.

RESULTS

A significant decrement was observed in 67% of patients, and was most common in the trapezius muscle (nine cases). The decrement of the trapezius muscle response ranged from 15.9% to 36.9%. The decrement was inversely correlated with the amplitude of compound muscle action potentials at rest. Neostigmine injection markedly improved the decrement in three patients, who showed noticeable decremental responses to 3-Hz RNS.

CONCLUSIONS

This study shows that myasthenic symptoms and abnormal decremental responses to low-rate RNS are common in X-BSMA.

Double trouble: spinal muscular atrophy type II and seropositive myasthenia gravis in the same patient

Autosomal recessive proximal spinal muscular atrophy is caused by deletions in the survival of motor neuron (SMN1) gene, while autoimmune myasthenia gravis is an acquired disorder. An association between these two diseases has not been reported. Our patient with intermediate spinal muscular atrophy (SMA type II) did not need alimentary or respiratory aid until age 51 when he suddenly developed bulbar weakness and respiratory insufficiency. Seropositive myasthenia gravis was confirmed and the corresponding symptoms resolved on treatment.