Why do I feel so weak?

37-year-old lady presented to ED with acute onset shortness of breath at rest but worsened with movements. She denies fever, sputum production, wheezing, chest pain, recent trauma, unintentional weight loss and lower limb swellings.

On further questioning, she stated that she has been suffering with (L) monocular double vision, difficulty walking worse following a period of physical activity and difficulty swallowing for the past 10 days which she is currently waiting for her GP appointment. She mentioned that her mobility improves after periods of rest.

Background: 9 weeks pregnant, type 1 diabetes mellitus (Well-controlled), hypertension (Life-style control)

No smoking history and only drinks about 2 pints of beer every weekend

Medications: Folic acid 5mg OD, Lantus injection

Family history: Mom diagnosed with Grave’s disease, no family history of ALS

Neonatal history: Up to date vaccinations, no neurodevelopmental issues

O/E:

Appears fatigued and tired but alert

A - Airway intact, no audible noises, able to complete sentences but appeared breathless at the end

B - Chest expands equally with accessory muscle usage

Respiratory rate of 18

Oxygen saturation of 88% on RA – improved to 98% on 15L/min NRB

Chest is clear on auscultation

Resonant on percussion

C - HS 1+2+0 regular

Blood Pressure 128/84

Heart Rate 89

D – GCS 15, left sided ptosis, nasal quality speech, restricted movement in left eye on lateral abduction, otherwise other cranial nerves were intact

RUL and LUL power 5/5 initially but following repetitive shoulder movements, the power reduced to 4/5 generally

Intact tone and reflexes, and sensation

LLL and RLL power 5/5 initially but following repetitive leg movements, the power reduced to 4/5 generally

Intact tone, reflexes, and sensation

E – Calves SNT with no ankle oedema, no skin changes, Blood sugar 7.1mmol/L

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Investigations:

Please interpret the CT brain, MRI brain and ECG.

Answers

Other investigations:

Spirometry

Forced Vital Capacity (FVC) at 69%

Forced Expiratory Volume at 1 second (FEV1) is 85%

FEV1/FVC is at 0.9

Arterial Blood Gas

pH – 7.31

pO2 – 8.1

PCO2 – 6.2

Bicarbonate – 24

Lactate – 0.8

Bloods

Hb 143

WCC 8.5

Plts 280

HBA1C 37

Adjusted Calcium 2.1

Serum sodium 148

Serum potassium 3.8

Urea 4

Creatinine 48

Egfr > 90

LFTs NAD

Ketones - 0.8

Blood sugar is 10.2 mmol/L

What would your diagnosis be? Pick one answer.

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  Exacerbation of Chronic obstructive pulmonary disease
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  Diabetic Ketoacidosis
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  Myasthenia Gravis
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  Stroke

See All Options

Answer

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Myasthenia Gravis (MG)

Overview

Autoimmune condition in which antibodies attack the acetylcholine receptors (AChRs) or muscle-specific kinase (MuSK) in postsynaptic muscle cells. Most cases are due to IgG1 and IgG3 antibodies.

Commonly affects woman below age of 40 with a known prevalence of 50 to 200 people per million

MG crisis occurred in about 20% of patients with MG precipitated by period of stressors such as infection, surgery, sudden changes in immunosuppressants and certain medications (beta-blockers and anti-arrhythmic)

10-20% associated with thymomas, hence the importance of CT-thorax to assess for thymomas (Typically an anterior mediastinal structure)

Children can be affected via:

- About 10-20% infants are affected with transient neonatal MG presenting with respiratory and feeding difficulties following birth

- Juvenile MG – similar presentation to MG but in younger patients. More common in females

- Congenital MG – Rare with prevalence of 1 in 200,000.

Differential Diagnoses

• Lambert Eaton disorder

• Guillain Barre syndrome

• Botulism

• Stroke

• Amyotrophic Lateral Sclerosis

• Multiple sclerosis

Diagnostic evaluation

• Diagnosis involves testing for AChR antibodies or MuSK antibodies as well as clinical assessment

• Electromyography to determine neuromuscular response following stimulation (Most sensitive diagnostic test)

• Edrophonium test (No longer done due to high complication rates as it can lead to life threatening bradycardia)

Management

• In CRISIS – Plasmapheresis, IV Immunoglobulins (IVIG) and high dose steroids can be considered

• Intubation may be required in MG crisis if acute Type 2 Respriatory Failure occurs

• Acetylcholinesterase inhibitors such as pyridostigmine

• First line Tx (If not in crisis) – Prednisolone with pyridostigmine +/- surgery if thymoma is present

10% of patients are treatment refractory

In which case, biologics such as mycophenolate, cyclosporine, methotrexate, cyclophosphamide and rituximab can be considered

Prognosis

• Prognosis tends to be favourable with most patients having normal life expectancy following immunosuppression

• About 33% of patients with known MG will have flare-ups during first trimester of pregnancy but improves during 2nd and 3rd trimester