I read with interest the recent case report on bilateral optic neuritis
due to isoniazid(1), and have the following comments to offer:
The patient described in the case was
receiving both isoniazid and streptomycin. The visual side
effects of isoniazid have been described in this report but
those due to streptomycin have been overlooked. The visual
complications described in literature during streptomycin
therapy include slowness of accommodation, trembling of distant
objects, continuance of image movement on turning the head,
disturbance of color vision, papilledema and optic neuritis(2).
Though uncommon, visual toxicity of streptomycin should have
been kept as a differential diagnosis in their patient.
Paradoxical reactions are commonly seen during
treatment of tuberculosis and steroids have been found to be useful in
their treatment. Optic neuritis as a paradoxical reaction to tubercular
allergen has been reported in adults(3). As the patient reported by them
responded to corticosteroids, the visual loss attributed to isoniazid
could be an immunologically mediated paradoxical reaction. I also
encountered a case where the patient developed optic neuritis on
anti-tubercular therapy; she was successfully managed with steroids, and
isoniazid was continued.
Thus, the patient described in this case report had a
clinical adverse event (optic neuritis) which in addition to isoniazid
therapy, could also be explained by concurrent disease (paradoxical
reaction) or the other drug (streptomycin). Taking into consideration the
above factors, the Naranjo algorithm for adverse drug reaction causality
assessment yields a score of 4 (and not 6 as per authors),
suggesting that the adverse drug reaction was only possibly
(and not probably) related to isoniazid.
References
1. Kulkarni HS, Keskar VS, Bavdekar SB, Gabhale Y.
Bilateral optic neuritis due to isoniazid (INH). Indian Pediatr 2010; 47:
533-535.
2. Walker GF. Blindness during streptomycin and
chloramphenicol therapy. Br J Ophthalmol 1961; 45: 555-559.
3. Monga PK, Dhaliwal U. Paradoxical reaction in
tubercular meningitis resulting in involvement of optic radiation. Indian
J Ophthalmol 2009; 57: 139-141.