Differentials
Bacterial gastroenteritis
SIGNS / SYMPTOMS
More prominent watery or bloody diarrhoea.
If systemic manifestations are present, they usually occur concomitantly with the gastrointestinal manifestations, rather than following them.
INVESTIGATIONS
Stool sample: cultures positive for Salmonella, Shigella, or Campylobacter; presence of white cells or lactoferrin.
Respiratory or gastrointestinal viral infections
SIGNS / SYMPTOMS
Myalgia and fever are common, but are usually associated with other respiratory (cough, coryza) or gastrointestinal (vomiting, diarrhoea) manifestations.
Outbreaks of viral infections are more common and widespread than those of trichinellosis.
INVESTIGATIONS
Diagnosis is usually clinical, based on brief self-limited course.
Viral antigens and cultures: positive in nasopharyngeal and bronchial samples in respiratory infections; positive in stool sample in gastrointestinal infections.
Glomerulonephritis
SIGNS / SYMPTOMS
In addition to fever, eosinophilia, and peri-orbital oedema, this condition causes haematuria and/or proteinuria, and renal failure. Occasionally, in severe cases of trichinellosis, glomerulonephritis can complicate the course of the disease.
INVESTIGATIONS
Urinalysis: presence of protein, blood, leukocytes, red blood cell (RBC) casts, and dysmorphic RBCs.
Serum creatinine: elevated.
Urea: elevated.
Kidney biopsy: shows inflammation, cellular proliferation, basement membrane thickening, fibrosis, and epithelial cell changes, and is confirmatory.
Anaphylaxis
SIGNS / SYMPTOMS
Hyper-acute presentation.
Peri-orbital oedema is normally accompanied by swelling of other mucosae (angio-oedema), hives, and possible respiratory distress.
INVESTIGATIONS
There are no confirmatory diagnostic tests.
Diagnosis is based on the clinical presentation and presence of a trigger factor.
Polymyositis and dermatomyositis
SIGNS / SYMPTOMS
Clinical course is more chronic.
Symmetric proximal muscle weakness is more common than myalgia.
Peri-orbital oedema may occur, but the rash in dermatomyositis is not transient.
INVESTIGATIONS
Electromyogram: short-duration, low-amplitude poly-phasic units on voluntary activation and increased spontaneous activity with fibrillations, complex repetitive discharges, and positive sharp waves.
Muscle biopsy: shows lymphocytic infiltrates, fibre atrophy, and necrosis, and (with electromyography results) is confirmatory.
Auto-antibodies: antinuclear antibodies, anti-Jo-1 antibodies, anti-signal recognition particle antibodies, and antibodies to Mi-2 may be positive.
Peri-orbital cellulitis
SIGNS / SYMPTOMS
Eyelid(s) are red and painful. Often unilateral.
Fever may be present, but there is no myalgia.
INVESTIGATIONS
There are no confirmatory diagnostic tests.
Diagnosis is usually clinical.
Blood cultures may occasionally be positive.
Orbital imaging (e.g., CT) may show inflammation of peri-orbital or orbital tissue.
Other parasitoses
SIGNS / SYMPTOMS
Several helminthic infections such as schistosomiasis, toxocariasis, and fascioliasis cause eosinophilia and may be confused with trichinellosis in the early stages.
INVESTIGATIONS
Stool sample: presence of ova or parasite.
Serum antibodies: may be positive for each specific parasite.
Infective endocarditis
SIGNS / SYMPTOMS
Infective endocarditis causes more persistent fever. Splinter haemorrhages present in late stages of the disease. Myalgias are usually not associated with muscle weakness.
Cardiac murmur is invariably present.
Other embolic or immune manifestations may be present.
INVESTIGATIONS
Echocardiogram: mobile vegetations on heart valves.
Blood cultures: positive.
Eosinophilia-myalgia syndrome
SIGNS / SYMPTOMS
Eosinophilia, myalgia, and cutaneous manifestations (rashes, pruritus) are common.
May occur in outbreaks and is usually associated with the consumption of L-tryptophan.
INVESTIGATIONS
There are no confirmatory diagnostic tests.
Leptospirosis
SIGNS / SYMPTOMS
Bi-phasic disease beginning with fevers, myalgia, rash, and gastrointestinal manifestations after contact with animal urine or faeces.
Followed by second phase with meningitis, liver, and renal failure.
INVESTIGATIONS
Blood cultures: positive for Leptospira species.
Enzyme-linked immunosorbent assay: positive for antibodies against Leptospira species.
Polymerase chain reaction: positive for Leptospira species.
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