Presentation of motor neuron disease in a patient with weight loss and acute-on-chronic respiratory failure

Background

Motor neuron disease (MND) is a neurodegenerative disorder that has a prevalence in the UK of 4–4.7 in 100 000.1 The term MND encompasses different forms of the disease, which patients may present with upper motor neuron and/or lower motor neuron signs. Spinal onset and bulbar onset MND represent most cases and typically manifest with progressive, unilateral weakness and stiffness in arms and legs. In a smaller proportion of patients who develop MND with respiratory onset, patients may present atypically, and its symptoms may be more insidious thus posing diagnostic challenges.

In this case, we describe the presentation of acute-on-chronic type 2 respiratory failure in a 72-year-old man under investigation for progressive shortness of breath on exertion (SOBOE), weight loss and lethargy. The case discusses the opportunities for potential earlier identification of neuromuscular disease as a differential diagnosis.

Case presentation

A previously fit and well 72-year-old retired man, first presented to his GP with a 6-month history of weight loss, lack of appetite, increasing fatigue, and shoulder and neck myalgia. Despite multiple investigations in the following 6 months from his first presentation, no cause of his symptoms was found. He was later referred to the hospital by his GP with worsening shortness of breath and intermittent confusion in the week leading up to his admission.

On further history taking, he reported worsening symptoms over the past 6 months with SOBOE, poor sleep at night and daytime sleepiness. He reported unintentional weight loss >1 stone with lack of appetite. He denied dysphagia, haemoptysis, changes in bowel habits or fever. He has no significant medical history and does not require any regular medications. There is no family history of malignancies. He is an ex-smoker with a 25 pack-year smoking history.

At the time of examination on the medical assessment unit, he had been started on a venturi mask for compensated type 2 respiratory failure.

On examination, the patient appeared cachectic. He was comfortable at rest but remained tachypnoeic with respiratory rate of 28, oxygen saturation (spO2) of 96% on 24% via venturi mask. Other observations were within normal limits. Neurological examination demonstrated scattered fasciculations in his hands, chest wall and anterior thigh and brisk reflexes. He was noted to have a weak ‘husky’ voice. Medical Research Council's (MRC) scale of muscle power was 5/5 throughout with sensation intact; he denied diplopia, and there was no ptosis.

A differential diagnosis of neuromuscular disorder was considered at the time; other causes such as chronic obstructive pulmonary disease and sleep apnoea were less likely but not excluded.

Investigations

From patient’s first presentation to the GP up to admission, he has had multiple investigations for his presenting symptoms and has been reviewed by different specialties (figure 1).

He was initially investigated for malignancy due to his smoking history; in addition, he was also investigated for inflammatory/rheumatological disorders, haematological disorders and coeliac disease. His blood tests initially showed polycythaemia, and CT Thorax, Abdomen and Pelvis (CT TAP) showed an incidental right retrosternal multinodular goitre. Otherwise, all investigations were unremarkable.

While he was undergoing investigations for weight loss and generalised weakness, he developed SOBOE.

Haematology and the ENT team have reviewed the patient, noting his general decline with shortness of breath at rest, worsening exercise tolerance and a weak cough. Following further investigations including an ultrasound scan of the neck and abdomen, nasoendoscopy and further blood tests, it was felt that he did not have a primary bone marrow disorder, and his symptoms were not caused by the goitre.

At the time of his spirometry, it was noted that his oxygen saturations were 93%, and the patient struggled to exhale for 6 seconds when measuring his forced vital capacity (figures 2 and 3). The outcome was suggestive of a restrictive pattern.

He was subsequently reviewed by a chest physician in a telephone clinic 3 weeks prior to his hospital admission; respiratory muscle tests, along with a ventilation-perfusion scan (V/Q scan) and an arterial blood gas (ABG) were arranged for further investigation.

On admission, he was found to have compensated type 2 respiratory failure on arterial blood gas (figure 4). MRI head and spine were normal. EMG and NCS were suggestive of MND (figure 5), probably the form of Amyotrophic Lateral Sclerosis (ALS) with no clear evidence of bulbar involvement.

The patient was started on non-invasive ventilation (NIV), a cough assist machine and a prophylactic percutaneous endoscopic gastrostomy (PEG) tube has been inserted to assist in nutritional intake. He has now been discharged and is being followed up by the home ventilation team and the MND team.