Differentials
Lyme disease
SIGNS / SYMPTOMS
History of tick bite with characteristic rash of erythema migrans. There may also be musculoskeletal manifestations such as arthralgia and arthritis; neurological manifestations such as cranial nerve VII or other cranial nerve palsies, aseptic meningitis, radiculoneuropathy; cardiovascular complications such as AV block, myopericarditis.
INVESTIGATIONS
ELISA or immunofluorescence assay, confirmed by a standardised Western blot assay.
Syphilis
SIGNS / SYMPTOMS
History of primary syphilis, typically with a painless genital ulceration. Optic neuritis can occur in secondary or tertiary neurosyphilis.
INVESTIGATIONS
Serological tests for syphilis.
HIV infection
SIGNS / SYMPTOMS
History of HIV infection; complications and secondary infections may be present.
INVESTIGATIONS
Serological tests for HIV.
Varicella-zoster
SIGNS / SYMPTOMS
History of chickenpox; optic neuropathy is more likely to develop in patients who are immunocompromised.
INVESTIGATIONS
Serological tests for varicella-zoster.
Aspergillosis
SIGNS / SYMPTOMS
Generally seen in immunocompromised patients. May be otherwise asymptomtic, or may cause haemoptysis; weight loss, chronic cough, and malaise. Other systemic involvement may be present.
INVESTIGATIONS
Serum Aspergillus galactomannan antigen by enzyme immunoassay positive in invasive disease; MRI or high-resolution CT of the brain may show focal lesions.
Cat-scratch disease
SIGNS / SYMPTOMS
Exposure to cats including bites, scratches, or any other contact. Papular, pustular, or crusted lesions at the site of inoculation, which usually occur around 3-10 days after exposure. Typically presents with painful, ipsilateral regional lymphadenopathy affecting a single node; however, optic neuritis (neuroretinitis) may be the only presenting feature.
INVESTIGATIONS
Serology (indirect fluorescent antibody or enzyme immunoassay) for Bartonella henselae may be positive; rapid diagnosis via PCR test may be helpful where available. Warthin-Starry silver stain is used to identify the organism in lymph node aspirate or biopsy.
SLE
SIGNS / SYMPTOMS
Typically causes multi-system manifestations that may include constitutional, musculoskeletal, mucocutaneous, renal, gastrointestinal, cardiac, and pulmonary features as well as neurological symptoms and signs.
INVESTIGATIONS
Positive antinuclear antibody in virtually all patients.
Sarcoidosis
SIGNS / SYMPTOMS
Typically causes non-specific pulmonary symptoms of cough and breathlessness. May also produce constitutional symptoms, arthralgias, photophobia.
INVESTIGATIONS
Diagnosis is confirmed by histology of affected organ showing non-caseating granulomas.
Behcet's syndrome
SIGNS / SYMPTOMS
Recurrent mouth ulcers plus 2 other clinical manifestations (recurrent genital ulcers, skin lesions, eye lesions, or positive pathergy test). Other organs may also be involved. There may be a family history, and it is more common in people of Mediterranean, Middle Eastern, and East Asian origin.
INVESTIGATIONS
No tests are specific for the disease.
Sjogren's syndrome
SIGNS / SYMPTOMS
Dry eyes (keratoconjunctivitis sicca) and dry mouth (xerostomia), caused by lymphocytic infiltration into the lacrimal and salivary glands. Can also be associated with dry skin, nose, throat, or vagina; arthralgias and myalgias; peripheral neuropathies; pulmonary, thyroid, and renal disorders; and lymphoma. Sometimes co-exists with autoimmune diseases (e.g., SLE, rheumatoid arthritis, systemic sclerosis).
INVESTIGATIONS
Diagnosis is chiefly clinical; anti-Ro (SS-A) and anti-La (SS-B) may be positive, but are not so in every patient, and they may be positive in other conditions.
Giant cell arteritis
SIGNS / SYMPTOMS
Most commonly seen in patients >50 years and typically accompanied by headache or jaw claudication.
INVESTIGATIONS
ESR raised (≥50 mm/hour); temporal artery biopsy typically shows granulomatous inflammation, sometimes with multinucleated giant cells.
Takayasu's arteritis
SIGNS / SYMPTOMS
Most commonly seen in women in their 20s or 30s. Systemic symptoms may be present but headache and cranial symptoms are usually not. Patients often have absent or asymmetrical peripheral pulses and multiple arterial bruits.
INVESTIGATIONS
Angiography, CT, or magnetic resonance angiography of the aorta and major arteries showing stenosis or occlusion.
Non-arteritic anterior ischaemic optic neuropathy
SIGNS / SYMPTOMS
Typically a sudden onset of diminished vision in a hemifield in one eye, often on waking. Most patients have vascular risk factors. Pain is usually not a feature, and the patient is generally otherwise asymptomatic.
INVESTIGATIONS
Diagnosis is usually by exclusion of arteritic causes of visual loss.
Drugs and toxins
SIGNS / SYMPTOMS
Optic neuropathies caused by drugs or toxins need to be considered in patients receiving treatment with tamoxifen, ethambutol, tetracycline, quinine, amiodarone, and disulfiram. Other toxins include methyl alcohol, radiation, and lead. The time course is chronic (except for acute methanol intoxication), and pathology is non-inflammatory.
INVESTIGATIONS
Funduscopy shows optic atrophy; MRI does not show enhancement of optic nerve.
Leber's hereditary optic neuropathy
SIGNS / SYMPTOMS
A maternally inherited mitochondrial DNA disorder that affects primarily the optic nerves. Leber's hereditary optic neuropathy (LHON) can mimic ON. Visual loss is ultimately bilateral, either simultaneous at onset or sequential within 1 year. The temporal pattern of visual loss may be similar to ON, and visual acuity is often reduced to finger counting. Pain is seldom a feature of LHON. Occasionally there are associated subtle neurological abnormalities or white matter changes on MRI. Female carriers with a disease very similar to multiple sclerosis (MS) (with prominent binocular visual loss) have a LHON/MS overlap syndrome known as Harding's disease.[37]
INVESTIGATIONS
Funduscopy acutely shows pseudo-oedema of the optic disc and peripapillary micro-angiopathy, which can be present in pre-symptomatic stages. More than 90% of familial cases are positive for primary LHON mutations affecting nucleotides 11778, 3460, or 14484 in mitochondrial genes involved in oxidative phosphorylation, a critical process in cellular energetics.
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