Differentials
Contact dermatitis
SIGNS / SYMPTOMS
Presents as a localized rash or irritation of the skin caused by contact with a foreign substance. The pain and the rash usually occur simultaneously.
INVESTIGATIONS
Eliminating exposure to the irritating agent usually results in symptom resolution.
Herpes simplex
SIGNS / SYMPTOMS
Grouped vesicles on an erythematous base in a nondermatomal pattern, often preceded by pruritus and pain. Oral and genital lesions most common.
INVESTIGATIONS
Polymerase chain reaction (PCR) of sample from lesions.
Cholecystitis
SIGNS / SYMPTOMS
Presents with pain in the right upper quadrant of the abdomen, accompanied with nausea, vomiting, and fever. On examination, patients may have Murphy sign.
INVESTIGATIONS
Patients have elevated levels of alkaline phosphatase, bilirubin, CRP, and WBCs. Ultrasound or CT scan may show a bile duct blockage, gallstones, and inflammation of the gallbladder.
Ulcerative keratitis
SIGNS / SYMPTOMS
Symptoms depend on the cause. Presents with pain and redness in the affected eye, with visual changes dependent on the ulcer location. Some may also present with purulent discharge. The distinctive feature that differentiates HZ from other causes is the development of rash in the affected dermatome.
INVESTIGATIONS
Fluorescein staining would show the presence of a dendritic ulcer if the cause is herpes simplex virus and is unrelated to HZ.
A slit-lamp examination would indicate other causes of ulcerative keratitis, such as a foreign body.
Glaucoma, acute angle-closure
SIGNS / SYMPTOMS
Presents with periorbital pain, blurry vision, and headache. However, there is no development of an accompanying rash in the dermatome innervated by the eye.
INVESTIGATIONS
Tonometry shows increased intraocular pressure (>20 mmHg), diagnostic of glaucoma.
Trigeminal neuralgia
SIGNS / SYMPTOMS
Presents with an intense, stabbing, electric shock-like pain in the areas of the face innervated by the trigeminal nerve. Patient may locate a trigger area for the pain. Patients do not develop a rash.
INVESTIGATIONS
No differentiating test is available.
Appendicitis, acute
SIGNS / SYMPTOMS
Typically presents with pain in the right lower abdominal quadrant. Additionally presents with nausea, vomiting, and sometimes signs of bowel obstruction, which are not present in patients with HZ. There is no accompanying rash with these symptoms.
INVESTIGATIONS
On CBC, WBCs are often elevated. CT scan would indicate inflammation of the appendix.
Renal calculi
SIGNS / SYMPTOMS
Presents with severe colicky pain and inability to lie still. Other symptoms include urinary frequency, blood in urine, and painful urination. Flank pain shows on examination. These symptoms are not accompanied by the development of a rash.
INVESTIGATIONS
A kidney, ureter, and bladder x-ray would show the location of the calculi.
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