Anisocoria

Monday I saw a patient who came to the clinic for follow up of a perirectal abscess. He is HIV+ with a past medical history of pulmonary tuberculosis. His current CD4 count is in the 300’s. As it turns out, his abscess had completely resolved, but he was complaining of back pain along his spinal cord that started in his lower back and continued all the way to the back of his head. He said that the pain was so unbearable at times, that he had to lie down. He occasionally felt nauseous, but had not vomited. He feels like he has had fevers in the afternoons, but he does not have a thermometer to measure the temperature (he was afebrile in clinic). He said that all of this started 5 or so days before he went to see the doctor for the abscess, but that it has been getting worse, and the headaches and back pains are progressive.

On physical exam, I first noted his prominent anisocoria. His left pupil was dilated (mydriasis) and his right pupil was constricted (miosis). In addition, it seemed that his left eye tended to abduct (look away from his nose) with forward gaze. His vision was markedly decreased in the left eye. On fundoscopic exam, the margins of the left optic disc were sharp, without any evidence of papilledema, but the retina appeared dark and dusky. I was unable to visualize the right retina, due to miosis. Additionally, bending the patient’s head to his chest caused severe back pain, as well as bending his knees toward his chest while lying on his back – positive meningeal signs. Otherwise, his physical exam was completely normal.

Positive meningeal signs usually merits a lumbar puncture, but since he had focal neurologic deficits, we decided to get a CT scan of his head first. After working with the social worker to find funding for a CT scan, the patient was able to get the scan Monday afternoon. Tuesday the results were back – single hypodensity seen in the right frontal lobe with minimal mass effect. The patient returned to clinic Tuesday for the results, and on further questioning, it was discovered that he has cats in his house.

So what is the differential diagnosis of the mass lesion?

- Primary CNS lymphoma
- Toxoplasmosis encephalitis
- Tuberculous encephalitis (Tuberculoma)
- VZV encephalitis
- Chagoma (Trypanosoma cruzii)
- PML

And he could also have cryptococcal, tuberculous, or fungal meningitis as well.

So what did we do? Well, with the minimal mass effect seen by the CNS lesion, the lumbar puncture was not performed. We ordered a serum cryptococcal antigen test, as a means of looking for cryptococcal meningitis without a lumbar puncture. And we started him on therapeutic dosages of pyrimethamine, sulfadiazine, and leucovorin for toxoplasmosis. The reality is, that there is not an acceptable diagnostic test for toxoplasmosis that is available in Guatemala, so treatment and assessment for improvement or worsening of symptoms with therapy is the way in which it is diagnosed or ruled out. There is not PCR for EBV either, which would be useful in diagnosing Primary CNS lymphoma. The patient has agreed to come to the clinic every day this week for neurological checks, and to assess for change in symptoms. What do you think he has?