PBP is nothing more than the early stage of bulbar onset amyotrophic lateral sclerosis (ALS). According to the revised El Escoral criteria PBP could be called “possible ALS with bulbar onset”. Symptoms are progressive and over time dysarthria gets more and more severe, finally leaving the patient anarthric. Dysphagia is part of the clinical picture and swallowing is increasingly difficult. Myasthenia gravis is of utmost importance to rule out, as this is a disease with therapeutic options.

Authors

M.M. van der Graaf, M.D.
J.H. Veldink, M.D., Ph.D.

Clinical features
Usually the patient with PBP presents with disturbed speech. Sometimes family or friends notice a change of speech before the patient does. Speech becomes slurred and sometimes nasal. The voice can get hoarse and loses volume. Symptoms are progressive and over time dysarthria gets more and more severe, finally leaving the patient anarthric. Dysphagia is part of the clinical picture and swallowing is increasingly difficult. Read more

Natural course and prognosis

There is no information available on the pure PBP subtype, as, again, systematic research on this subject is lacking. Bulbar onset ALS seems to carry a worse prognosis than limb onset ALS. ^{10, 12,13} However, as the incidence of bulbar onset ALS increases with age, and age is a strong independent prognostic factor, sometimes bulbar onset is not found to be an independent prognostic factor when matched for age. ¹⁴

Epidemiology

The phenotype of pure PBP is rare.  Mostly these are patients dying of another illness before a more general picture of motor neurone degeneration has had a chance to become manifest.⁴ No exact numbers can be given as systematic research on this subject is lacking. As for the bulbar onset type of ALS, it is known that 20%-30% of the cases of MND present with bulbar signs.^9,10 The bulbar onset type of ALS can occurs at any (adult) age but incidence increases with age.² There is a female preponderance in patients with bulbar onset ALS.^10,11

Differential diagnosis
Myasthenia gravis is of utmost importance to rule out, as this is a disease with therapeutic options. A history of fluctuations over the day, fatigability on neurological examination, antibodies against acetylcholine receptors, single fibre EMG of bulbar muscles and a Tensilon test can help to differentiate. 5 Early impairment of eye movements does not fit with a diagnosis of PBP but is often found in myasthenia gravis. A clinical picture dominated by pseudobulbar signs and symptoms such as a spastic dysarthria, exaggerated pseudobulbar reflexes and pseudobulbar affect (uncontrollable crying and or laughing) could also fit into a diagnosis of SAE or atypical parkinsonian syndromes such as progressive supranuclear palsy (PSP) of multiple system atrophy (MSA). Read more

Ancillary investigations

MR imaging to rule out structural lesions and vascular pathology is necessary. Laboratory tests focussed on diseases in the differential diagnosis can be necessary, as well as tests as defined in the revised El Escorial criteria.³ Needle EMG should be performed in search of lower motor neurone disease in the bulbar, but more importantly in the cervical, thoracic and lumbosacral region.³  Finding lower motor neurone disease in other regions indicates that the bulbar symptoms occur in the context of a more disseminated motor neurone disease.  Sometimes EMG is needed to exclude myasthenia gravis, where repetitive stimulation and/or single fibre EMG can be helpful. Sometimes analysis of the cerebral spinal fluid might be needed to rule out an inflammatory process like polyneuritis cranialis.

Therapy
When alternative diagnoses have been ruled out, and the PBP can be said to be a “possible ALS with bulbar onset” Riluzole can be considered. Although there is no literature available as this category of patients was not included in a large multicentre it seems a rational therapy as a similar pathogenesis is assumed. 15 Further therapeutic options are focussed on care aspects. A multidisciplinary approach involving (among others) speech therapy, occupational therapy and dietary care is recommended. A recent study found a positive effect of a multidisciplinary approach in MND on survival, the effect being most prominent in the bulbar onset group. Read more

References
1.      Duchenne de Boulogne G. Paralysie musculaire progressive de la langue, du voile du palais et des lèvres. Arch Gen Med 1860;16:283-296 and 431-445 Read more