Eyes Burning + Generalised Weakness in a 26-Year-Old Male: Clinical Approach

Priority Differential Diagnoses

1. Myasthenia Gravis (MG) - TOP PRIORITY

• MG is an autoimmune disorder targeting nicotinic acetylcholine receptors at the neuromuscular junction, causing fatigable muscle weakness that worsens with repetitive use and improves with rest.
• Ocular involvement occurs in 90% of cases and is the presenting feature in 60%. Two-thirds have both ptosis and diplopia. - Kanski's Clinical Ophthalmology, 10th ed.
• Onset in the third decade is classic, with symptoms including painless fatigue on exercise, proximal limb weakness, ptosis, diplopia, dysarthria, and dysphagia.
• Notably, "burning" eyes can occur from corneal exposure due to incomplete lid closure from orbicularis weakness.
• The mean age of onset in men is 42-49 years, but early-onset MG in young males does occur. - Bradley and Daroff's Neurology in Clinical Practice

2. Thyrotoxicosis / Graves' Disease

• Thyrotoxicosis causes eye discomfort, diplopia, fatigue, proximal muscle weakness (pelvic and shoulder girdle), tachycardia, weight loss, tremor, and heat intolerance. - Frameworks for Internal Medicine
• Graves' ophthalmopathy causes periorbital/conjunctival edema, erythema, proptosis, eyelid retraction - all of which can produce a "burning" sensation. - Tietz Textbook of Laboratory Medicine, 7th ed.
• Younger patients more commonly show hyperadrenergic manifestations (anxiety, restlessness, tremor). - Frameworks for Internal Medicine
• Important: MG and Graves' disease coexist more than expected by chance alone. - Bradley and Daroff's Neurology
• Diagnosis: Serum TSH (suppressed), free T4 (elevated), TSH receptor antibodies.

3. Organophosphate / Chemical Toxicity

• Organophosphates (used as pesticides, herbicides, lubricants) inhibit acetylcholinesterase, producing acute cholinergic syndrome: lacrimation, burning eyes, weakness, nausea, salivation, headache, bronchospasm. - Bradley and Daroff's Neurology
• Absorption can occur via skin, inhalation, or GI tract - ask about agricultural or occupational exposure.
• More severe: bradycardia, chest pain, diarrhea, pulmonary edema, convulsions, coma.
• Treatment: Pralidoxime 1g IV + Atropine 1mg SC every 30 min until secretions controlled.

4. Infectious / Viral Illness

• Viral conjunctivitis + systemic viral syndrome (adenovirus, EBV, influenza) commonly presents with burning red eyes, fever, myalgia, and generalised weakness.
• Usually accompanied by prodromal symptoms, lymphadenopathy, fever.

5. Systemic Lupus Erythematosus (SLE)

• Can cause sicca syndrome (dry, burning eyes from secondary Sjogren's), uveitis, and profound fatigue/weakness.
• More common in women, but males can be affected.
• Screen with ANA, anti-dsDNA.

6. Anaemia

• Severe anaemia causes generalised weakness, fatigue, pallor, and eye symptoms (conjunctival pallor; rarely, high-output state causes pulsatile tinnitus or visual symptoms).

Key Differentiating Questions (History)

Examination Priorities

1. Eyes: Ptosis? Diplopia? Proptosis? Conjunctival injection? Lacrimation? Pupil size (miosis = cholinergic, mydriasis = sympathomimetic)
2. Fatigability test: Ask patient to look up for 2 minutes - ptosis worsening = MG (Simpson test positive)
3. Neck: Goiter, bruit
4. Thyroid signs: Tremor, tachycardia, warm moist skin, lid lag, exophthalmos
5. Power: Proximal > distal weakness pattern (myopathic/MG pattern)
6. Vital signs: Bradycardia (cholinergic toxicity), tachycardia (thyrotoxicosis)
7. Secretions: Excessive salivation, lacrimation (organophosphate)

Initial Investigations

When to Act Urgently

• Myasthenic crisis: Dysphagia + dyspnoea + weakness = intubate and manage in ICU
• Thyroid storm: Fever + tachycardia + altered consciousness = life-threatening emergency
• Acute organophosphate poisoning: Bradycardia + bronchospasm + pinpoint pupils = atropine + pralidoxime immediately

Bottom line: In a 26-year-old male, the combination of burning eyes and generalized weakness most warrants early screening for Myasthenia Gravis (fatigable weakness, ocular involvement) and Thyrotoxicosis/Graves' disease (eye symptoms + proximal weakness + hypermetabolic features). Organophosphate toxicity must be excluded if there is any occupational or environmental exposure history. A careful history focusing on symptom fluctuation through the day and associated features will guide workup.